Methods adapted to evaluate products for textured hair: Shine, curl shrinkage, flexibility and consumer‐perceived hair porosity

Abstract

Objective

This work presents adapted methods for quantifying hair shine, shrinkage, flexibility and consumer‐perceived porosity in textured hair.

Methods

• The shine evaluation method utilizes image analysis of standardized hair tresses under controlled lighting conditions. A custom‐built imaging chamber minimizes extraneous light, while a macro written for ImageJ isolates and quantifies shine points based on grayscale thresholding. Additionally, hair greying caused by sebum or product application is evaluated by analysing the darkest and brightest pixels.

• Curl shrinkage profiles are assessed using imaging and image analysis techniques, allowing hair length changes to be evaluated as a function of humidity, product application and time. A three‐point bending technique was adapted to assess curl stiffness or flexibility in type 4 hair products.

• Contact angle measurement was refined to measure consumer‐perceived hair porosity. This included designing an adapter to securely fix textured hair during testing and recording video frames for improved measurement precision.

Results

• Shine evaluation method: The region of interest ROI and shine evaluation parameters less sensitive to curl pattern were proposed. Hair greying was found to depend largely on the loss of bright colour during light reflection. Effective shine treatments not only improved shine but also restored hair colour vibrancy by enhancing the darkest and brightest shades.

• Curl shrinkage test method: Testing was standardized at 30% and 60% relative humidity. For type 3 hair, an appropriate test duration at 60% humidity was 6 h, while for type 4 hair, it was 8 h. Reduced hair tress mass (e.g. 0.25 g) minimized length evaluation challenges in type 4 hair and type 3 tresses.

• Three‐point bending technique: Despite excellent curl shrinkage management properties, certain fixative products (e.g. gels) significantly increased hair stiffness, while others of similar efficacy maintained flexibility comparable with virgin hair.

• Contact angle method adaptation: Consumer‐perceived surface porosity was evaluated in differently treated type 4 hair. Repeated heat damage did not alter this parameter. Oxidized hair exhibited similarly low surface hydrophobicity, which was lower than that of relaxer‐treated hair.

Conclusions

The methods discussed demonstrate their suitability for evaluating the ability of products to influence textured hair shine, shrinkage management, flexibility and consumer‐perceived porosity.

The study introduces new lab methods to measure shine, curl shrinkage, stiffness and surface wetting in textured hair. These tools help assess how products and treatments affect the hair's visual appearance and response to humidity or damage.

INTRODUCTION

The science of hair testing has long been established for straight, wavy and occasionally curly hair, with numerous standardized methods available to evaluate hair appearance and other properties. These methods have been employed to characterize hair and serve as tools for testing hair care actives and formulations. However, as cultural preferences evolve, wavy, curly and coily hair types now represent a significant force in the market, with increasing numbers of individuals embracing their natural hair patterns. This shift underscores the growing need for inclusivity and representation in hair care product testing.

Shiny hair is often synonymous with healthy hair, as consumers aspire to achieve a natural sheen while avoiding the dullness associated with ‘dead’ or damaged hair [1]. Consequently, quantifying hair shine has become a popular technique among formulators to evaluate how their products remove sebum and other particulates that accumulate on unwashed and untreated hair [2]. Instruments such as the Bossa Nova Vision SAMBA and other methods for measuring reflected light, or lustre, in straight hair types have provided valuable insights using multiple shine parameters to substantiate product claims and guide product development [3, 4]. McMullen and colleagues [5] studied the natural configurations of African‐descendant hair and introduced foundational insights into novel imaging techniques for evaluating coily hair shine. Using Image Tool 2.0 software, they quantified the number and shape of reflections and analysed the distribution of black‐and‐white pixels in images of clean and sebum‐treated hair. However, these evaluations were performed on thresholded images, potentially concealing part of the story.

The challenge of maintaining elongated curls is the opposite of the experience faced by individuals with artificially curled hair. A straightforward parameter for evaluating curl length, proposed by Loussouarn and colleagues [6], involves measuring the length of hair in its natural configuration compared with its elongated configuration, commonly referred to as the ‘curl index’. However, the literature provides little to no discussion on the specific conditions for such testing.

Styling product testing for hair assembly stiffness, flexibility and plasticity has long been investigated using methods such as bending hair fixed into omega loops [7] or performing full tress tests with the three‐point cantilever bending technique [8]. These techniques typically evaluate hair fixative properties, often on straight or slightly wavy hair. The three‐point bending method using full tresses is more user‐friendly than the omega loop method [8]. Given that managing coily hair often requires greater effort, the products with stronger effects may affect hair flexibility, which may not always be a desired outcome. Thus, testing products for this property should align with the product's original purpose, such as curl shrinkage management. To our knowledge, no peer‐reviewed literature discusses the use of the three‐point bending technique to assess products for textured hair.

Consumer‐perceived hair porosity, often discussed in mainstream hair care circles, refers to the degree to which substances penetrate hair fibres. Increased hair damage through heat and/or bleaching treatments is believed to this parameter. While extensive work exists on European hair types, particularly using the Wilhelmy plate method [9], limited information is available for textured hair, partly due to the challenges posed by its curlier structure, which makes manipulation to maintain a flat surface more difficult. The Wilhelmy plate method has been used to calculate the dynamic contact angle of single fibres [9], but it is a tedious and time‐consuming approach to assessing hair hydrophobicity. Zur Wiesche and colleagues developed a method to evaluate the contact angle between a hair bundle and water via imaging and measuring the angle between a water droplet and the hair. However, this method is limited, as the contact angle could not fall below 80 degrees, restricting its applicability in hair science and product testing. Coderch et al. used this method to determine the contact angle of curly hair for the first time [10], but the level of hair damage in their study did not exceed the limitations described by Zur Wiesche.

This work systematically adapts and validates image‐based shine analysis, curl shrinkage profiling, three‐point bending and contact angle measurement for Walker type 3 and type 4 textured hair, establishing protocols suitable for product evaluation and claims substantiation.

MATERIALS AND METHODS

Substrate

For shine study, three‐point bending study, and contact angle measurements, a single‐source, Walker type 4 virgin hair was procured from TSEBO Manufacturing and Technical Services (Johannesburg, South Africa) and bound in‐house into 1 g tresses (example in Figure 1).

FIGURE 1.

1 g curl type 4 hair tress.

Fur curl elongation studies, a single‐source, types 3 and 4 virgin hair was purchased from International Hair Importers and Products (Glendale, NY, USA) and TSEBO Manufacturing and Technical Services (Johannesburg, South Africa), and bound in‐house into 0.25 g tresses (examples in Figure 2), and used for curl elongation study.

FIGURE 2.

Different curl type tresses of 0.25 g: (a) Curl type 3 and (b) Curl type 4.

It is worth noting that 1 g type 3 tresses treated with products failed to dry fully within 24 h, likely due to increased water retention and reduced airflow. 1 g type 4 tresses dried into irregular, variable shapes, which hindered reproducible length measurements.

Test products

For the shine, curl elongation and three‐point bending studies, we used commercially available products. The ingredients are listed in the Supporting Information File S1.

Artificial sebum (Dust Sebum Emulsion) was purchased from Scientific Services S/D Inc. (Sparrow Bush, NY, USA) and diluted with deionized water to achieve concentrations of 10% and 50%.

Commercially available products, including non‐conditioning Salon Care Clear 40 vol developer and Professional BW2 lightener powder (Clairol, Italy), Dark Auburn hair dye (L'Oreal Paris, USA), Dark and Lovely Relaxer (Soft Sheen Carson, USA), hair dryer (Remington, Middleton, WI, USA) and flat iron (Conair Corporation, NY, USA), were purchased for the contact angle study.

A 15% SLES solution was prepared by mixing deionized water with sodium lauryl ether sulphate (BASF, Ludwigshafen am Rhein, Germany) and adjusting the pH to 5.2 using citric acid and sodium hydroxide (Sigma–Aldrich, Burlington, MA, USA).

Hair treatments

All commercial product treatments were performed using an intellifaucet set at 40 ± 2°C with a controlled rate of 1 GPM (gallon per minute).

Hair treatments used for contact angle measurements

Hair bleaching

Mix powder and 40 vol developer at a 2:1 ratio. Apply 5 g of bleach per 1 g tress, massage thoroughly and cover the hair with foil. Process once at 40°C for 35 min.

Hair blow drying

Wet hair for 30 s. Blow dry using medium heat and high velocity with a round brush for 4 min per cycle. Repeat for 26 cycles to simulate half a year of once‐weekly use.

Hair flat ironing

Flat iron dry hair at 232°C using 30 passes at 6 s per pass per cycle. Repeat for 26 cycles to simulate half a year of once‐weekly use.

Hair dyeing

Set the hot plate to 27°C. Prepare the commercial colourant mixture and apply 5 g dye per 1 g tress. Distribute evenly from root to tip and turn the tress after 10 min. Process for a total of 20 min. Rinse until water runs clear.

Hair relaxation

Set the hot plate to 35°C. Prepare the relaxer cream and activator mixture. Apply 5 g relaxer per 1 g tress and distribute evenly from root to tip. Comb 3× and repeat the combing strokes after 5, 10 and 15 min of residence time to mechanically straighten the hair during processing. Process for 20 min. Rinse thoroughly for 2 min.

Apply 0.25 mL of post‐treatment, process for 10 min and rinse for 30 s. Apply 0.25 mL of neutralizing shampoo, massage for 30 s and rinse for 30 s. Apply 0.25 mL of moisture mask, process for 5 min and rinse for 30 s.

Treatment of relaxed hair

Treat wet hair with 0.1 mL conditioning wash per tress, massage for 30 s, process for 1 min and rinse for 30 s. Apply 0.15 mL conditioner per tress, massage for 30 s, process for 5 min and rinse for 30 s. Allow tresses to dry overnight at 30% ± 2% RH and 22 ± 2°C.

Hair treatments used for shine, curl shrinkage and three‐point bending tests

Shampoo/conditioner/mask application

Wet hair for 30 s, apply product at a dosage of 0.4 mL/g hair, massage throughout the tress for 30 s and rinse.

Conditioning leave‐in product application

Wet hair for 30 s, apply leave‐in at a dosage of 0.15 mL/g or 0.2 mL/g hair and massage throughout the tress for 30 s.

Shine serum application

Apply leave‐in on sebum‐treated hair at a dosage of 0.4 mL/g hair and gently massage throughout the tress for 30 s.

Sebum application

Spraying method:

Tresses were weighed after every three sprays to measure the amount of sebum applied. The tresses were flipped before each subsequent spray to ensure even distribution of sebum throughout the tress.

Dotted application method:

Sebum was applied in discrete droplets using a syringe, ensuring coverage of the entire area on both sides of the tress. The applied solution was then gently patted into the fibres to evenly coat and distribute the sebum.

Test methods

Shine test method

Hair shine was evaluated using image analysis of hair tresses imaged under controlled illumination conditions. Specular reflection points produced by the hair surface were quantified using various parameters to evaluate differences in shine and colour vibrancy.

Image acquisition

A custom darkroom chamber (16 × 25 in.) was constructed to house a Canon DSLR camera (Canon, Japan) and LED light panels (Viltrox, China) (Figure 3). A black velour fabric sheet was used as a backdrop for the hair tresses to minimize erroneous light reflections. Hair tresses were hung in the shine box at a distance of 12 in and an angle of 45° from each light source.

FIGURE 3.

The shine box, constructed internally, provides a light‐proof environment for imaging tresses at each stage of the treatment process.

Prior to the imaging, hair tresses were air‐dried at 22 ± 2°C and 60% ± 2% relative humidity (RH) for at least 8 h.

Six replicates were acquired for each tress. For studies evaluating curl pattern and sebum application, nine tresses per group were tested, while six tresses per group were used for commercial product testing.

Image analysis

Images were analysed using a custom macro in ImageJ version 153.e (NIH, Bethesda, MD, USA) with batch processing. Images were first cropped to a standardized region of interest (ROI). Two ROI sizes were initially evaluated:

• ROI 1: 1150 × 900 pixels.

• ROI 2: 250 × 250 pixels.

All data presented in this study were generated using ROI 2 (250 × 250 pixels) because preliminary testing showed that this smaller ROI reduced variability associated with differences in tress shape. The macro applied grayscale thresholding to isolate specular reflection points. The following parameters were extracted:

Count: The total number of shine points on the hair tress within the selected ROI.

Percentage: The percentage of the image area occupied by the shine points.

Average size: The average size of the shine points, measured in pixels.

Intensity: The black‐and‐white intensity of the shine points.

Colour vibrancy analysis

To evaluate changes in perceived hair colour vibrancy, additional analyses were performed on non‐thresholded images. Pixel intensity distributions were analysed across the grayscale range (0–255). Two regions were examined:

• Dark pixels: grayscale values 1–15

• Bright pixels: grayscale values 100–255

Cumulative count is the total number of pixels within a specific greyness range calculated using the equation below:

$$\text{Cumulative Count}=\sum _{\text{grayness}=G_{\min }}^{G_{\max }}\text{count}\left(\text{greyness}\right),$$

where

• Greyness is the pixel intensity level (1–255).

• Count (greyness) is the number of pixels at each greyness level.

• G _min is a minimum greyness level in the range.

• G _max is a maximum greyness level in the range.

Weighted count emphasizes the importance of specific greyness levels by assigning weights. The equation below calculates the weighted count for the darkest pixels:

$$\begin{array}{c}\text{Weighted Count}\left(\text{emphasizing darker pixels}\right)\hfill \\ =\sum _{\text{grayness}=G_{\min }}^{G_{\max }}\frac{\text{count}\left(\text{grayness}\right)}{\text{grayness}}.\hfill \end{array}$$

The equation below calculates the weighted count for the brightest pixels:

$$\begin{array}{c}\text{Weighted Count}\left(\text{emphasizing brighter pixels}\right)\hfill \\ =\sum _{\text{greyness}=G_{\min }}^{G_{\max }}\text{count}\left(\text{greyness}\right)\times \text{grayness}.\hfill \end{array}$$

These parameters were used to evaluate changes in hair brightness and darkness associated with sebum deposition and shine improving treatments.

Curl shrinkage evaluation method

Curl shrinkage was quantified by imaging drying textured hair tresses under controlled environmental conditions and measuring the change in apparent tress length over time. The method evaluated both shrinkage kinetics (time‐dependent behaviour) and the final equilibrated shrinkage after drying.

Hair handling for elongation test

Even after a few minutes of resting, coily hair tends to shrink significantly. To minimize shrinkage differences among the tresses during imaging, hair samples were treated in groups of five. Hair tresses were mounted on a bar, as shown in Figure 4a, then wetted and rinsed in groups of five. Treatment application and massaging were performed with the bar fixed horizontally (to free up both hands), as illustrated in Figure 4b.

FIGURE 4.

Hair mounting for: (a) rinsing and (b) product application and massage.

Image acquisition and analysis

The treated tresses were suspended in an environmentally controlled chamber (Figure 5) and imaged over 9.5 h at 15 min intervals using a Canon DSLR camera equipped with Digital Photo Professional 4 software (Canon, Japan). For each treatment group, five replicates were tested.

FIGURE 5.

Experimental set‐up for hair length evaluation.

Tress length was determined using in‐house‐developed LabVIEW software (NI, Debrecen, Hungary). The software output was exported as text files and transferred into Excel for processing. Curl shrinkage was calculated as percent length change relative to the initial (wet) length using:

$$\text{Change in length}=\left(\frac{\text{final length}}{\text{initial length}}-1\right)\times 100.$$

Three‐point bending test

Three‐point bending was used to evaluate the mechanical resistance and flexibility of hair tresses. The method measures the force required to bend a tress when compressed between two supports and a centrally positioned probe (Figure 6).

FIGURE 6.

Illustration of the technique and the machine setting.

Treated hair tresses were conditioned overnight at 22 ± 2°C and 60% ± 2% RH prior to testing. Eight tresses were tested per sample group. Tresses were mounted to the TA Texture Analyser's (Stable Micro Systems, UK) three‐point bending fixture. The probe pushed the tress down up to 1 cm. The first compression cycle was used for analysis. The area under the curve represents the energy required to bend the tress. Higher energy values indicate greater resistance to deformation (reduced flexibility).

Contact angle measurement

Contact angle measurements were used to evaluate the wettability of hair surfaces following different treatments. Lower contact angles indicate increased wettability, while higher angles indicate more hydrophobic surfaces.

Contact angle measurements were obtained using the Rame‐Hart Goniometer Model 190 F2 (Ramé‐Hart Instrument Co., USA). To accommodate the irregular geometry of textured hair, a custom‐designed bundle holder was used to align and stabilize the fibres during measurement (Figure 7). The sample holder incorporated a two‐clamp system. The primary clamp, fabricated in‐house, consisted of custom‐cut steel blocks and a threaded rod, providing a secure attachment to the goniometer platform. This steel assembly interfaced with a commercially available clamp fitted with a 3D‐printed end cap.

FIGURE 7.

Adapter to fix textured hair for contact angle measurements.

Prior to the measurements, hair was equilibrated overnight at 22 ± 2°C and 30 ± 2% RH. For each treatment group, five bundles of hair, each weighing 0.15 g, were prepared. Each bundle was secured to one side of the goniometer plate with a clamp adapter, manually stretched across the plate and clamped to the opposite side using a second adapter. Any stray or loose fibres within the imaging field were removed. DROPimage CA software (Ramé‐Hart Instrument Co., USA) was used to monitor hair and water droplets (the software does not allow video recording).

A syringe was used to deposit 1 μL of water onto the hair surface. The water deposition and spreading were recorded at 120 frames per second using Bandicam Screen Recorder software (Bandicam Company, Korea), capturing the field of view from immediately before droplet contact until 10 s after release from the syringe. Two droplets were recorded for each bundle, yielding a total of 10 measurements per test group.

Individual frames were extracted from the video recording. Contact angles were measured immediately after the initial water contact and at 1–6 s post‐contact using ImageJ software. The right and left contact angles were averaged to produce a single data point.

Statistical analysis

For all explored parameters, graphs were generated using Statistica version 12 (StatSoft Inc., Tulsa, OK, USA) and Microsoft Excel of Microsoft 365 (Microsoft Corporation, Redmond, WA, USA). Data are presented as means with standard errors of the mean. JMP analytical software version 17 (JMP Statistical Discovery LLC, Cary, NC, USA) was used to perform Student's t‐tests with a 95% confidence interval for experiments involving two treatment groups and Tukey's Honest Significant Difference (HSD) test for all‐pair comparisons in experiments with three or more groups. p‐values less than 0.05 were considered statistically significant and are indicated using different letters for statistically different groups.

RESULTS AND DISCUSSION

Shine evaluation

ROI selection

Type 4 hair reorganized itself into irregular configurations upon drying, leading to high morphological variability across tresses (Figure 8a). Initial analysis of the full tress imaging field resulted in noisy data with elevated intra‐group variability, requiring a large number of tresses per group, which was unsustainable due to the scarcity of supply. Subsequent evaluation of a restricted ROI of 250 × 250 pixels mitigated the impact of tress shape (data not shown) and reduced the number of replicates required for the test to six. Representative images illustrating the full field of view and the selected 250 × 250 pixel ROI are presented in Figure 8a,b, respectively.

FIGURE 8.

(a) ROI 1 cropped image and (b) ROI 2 cropped image.

Effect of curl pattern and parameters selection for the further study

To explore the effects of curl tightness and hair colour on the calculated shine attributes, preliminary evaluations were conducted using type 4 hair. Four groups (cells) of hair were compared (Figure 9):

• Cell 1: Type 4 tight curl, black hair.

• Cell 2: Type 4 tight curl, brown hair.

• Cell 3: Type 4 looser curl, brown hair.

• Cell 4: Type 4 tight curl, black hair.

FIGURE 9.

(a) Cell 1: Type 4 tight curl black hair, (b) Cell 2: Type 4 tight curl black brown hair, (c) Cell 3: Type 4 looser curl dark brown hair, (d) Cell 4: Type 4 looser curl black hair.

The images were thresholded, and shine attributes, including average reflection point size, number of reflection points and percentage area occupied by reflection points, were quantified. Results for average reflection point size are shown in Figure 10.

FIGURE 10.

Average size of shine points as a function of tress curl pattern and colour: Cell 1: Type 4 tight curl black hair, Cell 2: Type 4 tight curl black brown hair, Cell 3: Type 4 looser curl black brown hair, Cell 4: Type 4 looser curl black hair. The images incorporated in the graph are for visualization purpose. They do not represent the area tested during the experiment. Different letters label statistical differences measured using the Tukey HSD test.

The average size of shine points in type 4 hair was primarily influenced by curl tightness rather than colour. The larger parameter values were observed in looser curl hair (Cell 3) compared with tighter curl hair (Cells 1, 2 and 4) (Figures 10 and 11). No consistent pattern was observed in differentiating hair by colour.

FIGURE 11.

Raw images and thresholded images isolating shine points for (a) Cell 1 and (b) Cell 4 illustrating the change in shine point size as a function of curl/coil tightness.

The reflection count results are presented in Figure 12.

FIGURE 12.

Count of shine points as a function of tress curl pattern and colour: Cell 1: Type 4 tight curl black hair, Cell 2: Type 4 tight curl black brown hair, Cell 3: Type 4 looser curl black brown hair, Cell 4: Type 4 looser curl black hair. Different letters label statistical differences measured using the Tukey HSD test.

The statistical analysis revealed that the count of shine points in type 4 hair was not influenced by curl size or colour. The results for the percentage of the area occupied by reflection points are presented in Figure 13.

FIGURE 13.

Percent area occupied by shine points as a function of tress curl pattern and colour: Cell 1: Type 4 tight curl black hair, Cell 2: Type 4 tight curl black brown hair, Cell 3: Type 4 looser curl black brown hair, Cell 4: Type 4 looser curl black hair. Different letters label statistical differences measured using the Tukey HSD test.

Further statistical evaluation confirmed that the percentage area occupied by shine points was unaffected by curl tightness or colour. These findings indicate that the count and percentage area occupied by the shine points are relatively robust to variations in curl morphology and pigmentation within type 4 hair.

It is important to note that baseline variability in shine parameters among hair bundles could significantly influence treatment‐induced changes. To mitigate this and enhance inter‐group comparability, prescreening of washed and dried hair bundles is recommended prior to assigning tresses to treatment groups. Baseline shine parameters should be quantified for each bundle, followed by ranking the tresses according to their initial values and sequential redistribution across groups. This systematic balancing approach effectively equalizes both means and distributions, minimizing baseline differences. Post‐redistribution equivalence should be confirmed through appropriate statistical testing (e.g. ANOVA or equivalence tests for means and variances).

Effect of sebum application

The clinical study published in this series demonstrates that type 4 hair is the most diverse in terms of the number of days between hair washing [11]. The authors revealed that it is more common to wash this hair type less frequently than once a week, which suggests that sebum and particulate matter from the environment may reduce hair shine. Furthermore, a preliminary study showed that leave‐in conditioners reduce hair shine by 40%–60%.

A dust sebum emulsion was used to mimic the dulling effect of sebum and leave‐in conditioners, serving as a negative control for substantiation studies. Two concentrations of dust sebum emulsion, two application methods and three dosage plans were assessed to find the method that delivers the most reproducible outcome:

10% dust sebum solution

• 0.5 gram spray

• 0.5 gram dotted

• 1 gram spray

• 1 gram dotted

• 1 gram spray applied in 2 doses

• 1 gram dotted applied in 2 doses

50% dust sebum solution

• 0.5 gram spray

• 0.5 gram dotted

• 1 gram spray

• 1 gram dotted

• 1 gram spray applied in 2 doses

• 1 gram dotted applied in 2 doses

The results are presented in Figures 14 and 15.

FIGURE 14.

Count of shine points as a function of sebum treatment type and concentration.

FIGURE 15.

Percent area occupied by shine points as a function of sebum treatment type and concentration.

After sebum treatment, the count of reflections in all of the groups was statistically reduced compared with the baseline. The sebum treatment groups achieving 40%–60% reduction in count were as follows: Cell 1: 1 g Spray 2× 10% (41%), Cell 3: 1 g Drop 2× 50% (46%), Cell 3: 0.5 g Drop 50% (50%), Cell 3: 1 g Drop 2× 10% (50%), Cell 2: 1 g Spray 50% (52%) and Cell 1: 0.5 g Spray 50% (58%).

Similarly, the percent area occupied by the shiny dots in all sebum treatment groups was significantly lower than baseline. Treatment groups achieving 40%–60% reduction in this parameter were as follows: Cell 3: 0.5 g Drop 50% (46%), Cell 4: 1 g Drop 10% (47%), Cell 2: 1 g Spray 50% (48%), Cell 1: 1 g Spray 2× 10% (55%) and Cell 3: 1 g Drop 2× 10% (60%).

It is important to note that the dust sebum emulsion is a suspension; therefore, upon dilution, it is crucial to shake before each spray or sampling with a syringe. Qualitative observations indicated that while spraying provides a finer, more uniform mist, it results in greater material loss and potential contamination of the application workspace. Pooling at the tress base, a common issue with hair, was effectively mitigated by applying the total dose in two separate applications with intermediate drying (Figure 16).

FIGURE 16.

1 gram of sebum sprayed in one dose (a) vs. 1 g of sebum sprayed in two doses (b).

These results demonstrate that incremental dosing (e.g. 1 g as 2× 0.5 g) and drop application can enhance reproducibility and minimize artefacts in sebum‐induced dulling simulations for textured hair, supporting reliable substantiation of shine‐restoring claims.

Greying of the hair after sebum application

An interesting phenomenon was observed by analysing images for maximum and average pixel intensity parameters. While maximum intensity showed no consistent trend, average pixel intensity increased significantly in most sebum‐treated tresses compared with their baselines (Figure 17). This increase in pixel intensity was found to coincide with the visual observation of increased greying, in addition to the intended dulling effect.

FIGURE 17.

Mean intensity of shine points as a function of sebum treatment type and concentration.

To further characterize the shift in tonal distribution, images were preliminarily analysed using MATLAB R2022a (MathWorks, Natick, MA, US) to produce histograms of pixel intensity at baseline and after sebum application (Figure 18). Pixel values range from 0 (pure black) to 255 (pure white). Baseline histograms exhibited a primary peak below 30 (corresponding to darker tones) and a secondary distribution in the higher range (100–255, brighter pixels). Meanwhile, the sebum‐treated hair pixel intensity was higher in the region 25–75. This redistribution confirmed a shift toward overall greying, consistent with the deposition of dust sebum emulsion as a shine‐reducing and greying agent (Figure 18).

FIGURE 18.

Example pixel histogram from MATLAB showing the baseline image histogram (blue) and sebum‐treated hair image histogram (orange), highlighting the shift of pixel intensity instances to the grey pixel values after sebum application. 0 indicates the darkest pixel, and 255 indicates the whitest pixel.

Characteristics of colour vibrancy

The Cambridge Dictionary defines vibrancy as the colour quality of being bright and strong [12]. To extrapolate this definition to our findings, the blackest pixels (0–15 out of 0–255) represent the richest (strongest) black colour, and the pixels 100–255 represent the area used for colour brightness analysis. Cumulative pixel count and weighted pixel count were calculated for these regions, and the results are presented in Figures 19 and 20.

FIGURE 19.

Cumulative count of the blackest pixels, evaluated in the region of 1–15 (a) and brightest pixels, evaluated in the region of 100–255 (b). Different letters label statistical differences determined using Student's t‐test.

FIGURE 20.

Weighted count of the blackest pixels, evaluated in the region of 1–15 (a) and brightest pixels, evaluated in the region of 100–255 (b). Different letters label statistical differences determined using Student's t‐test.

Student's t‐test analysis confirmed a statistically significant difference between the baseline and sebum‐treated hair groups. The cumulative count of the darkest pixels is reduced by 33%, while that of the brightest pixels is reduced by 37%.

The weighted count after sebum treatment is reduced by 24% for the darkest pixels and 40% for the brightest pixels. The differences are statistically significant.

These comparable reductions across cumulative and weighted counts indicate a substantial loss in colour vibrancy, consistent with the observed greying and dulling effects of dust sebum emulsion deposition. These changes in hair darkness and brightness were larger than those reported previously [5]. To optimize the methodology to a consumer‐relevant level, future experiments should evaluate these parameters using larger datasets and compare with human perception of vibrancy changes. Such validation would help determine which parameter more reliably captures consumer‐relevant differences in hair colour appearance.

Effect of on‐market treatment

As a concluding component of this study, commercially available shine serums were tested for their ability to restore shine and vibrancy in sebum‐dulled type 4 hair tresses, relative to baseline and negative control (50% dust sebum solution 2× application) conditions. The reflective point count and the percentage of the area occupied by these points are presented in Figures 21 and 22.

FIGURE 21.

Count of shine points as a function of shine serum treatment: Cell 1: Textured hair shine serum 1, Cell 2: Any hair shine serum 1, Cell 3: Any hair shine serum 2, Cell 4: Textured hair shine serum 2. The statistical analysis was performed to compare the average values of the parameters within each cell. Different letters label statistical differences measured using the Tukey HSD test.

FIGURE 22.

Percent area of shine points as a function of shine serum treatment: Cell 1: Textured hair shine serum 1, Cell 2: Any hair shine serum 1, Cell 3: Any hair shine serum 2, Cell 4: Textured hair shine serum 2. The statistical analysis was performed to compare the average values of the parameter within each cell. Different letters label statistical differences measured using the Tukey HSD test.

Sebum application consistently induced a statistically significant reduction in shine point count (53%–58% relative to baseline), confirming the reproducibility of the negative control model. The serum application on dull hair delivered a variable outcome:

• Cell 1: Textured hair shine serum 1—no impact on sebum‐treated hair and 62% reduction compared with baseline.

• Cell 2: Any hair shine serum 1—no impact on sebum‐treated hair and 58% reduction compared with baseline.

• Cell 3: Any hair shine serum 2—no impact on sebum‐treated hair and 72% reduction compared with baseline.

• Cell 4: Textured hair shine serum 2—improved the shine by 112% increase compared with sebum‐treated hair and was indistinguishable from the baseline.

The analysis of the percentage of the area occupied by reflective points provided comparable statistical differentiation to the count. Notably, textured hair shine serum 2 demonstrated a 175% improvement in the reflective area of sebum‐dulled hair.

To assess vibrancy restoration using textured hair shine serum 2, the images were analysed to obtain the cumulative and weighted counts of the darkest and brightest pixels. The results are presented in Figure 23.

FIGURE 23.

Cumulative count of the blackest pixels, evaluated in the region of 1–15 (a) and brightest pixels, evaluated in the region of 100–255 (b). Weighted count of the blackest pixels, evaluated in the region of 1–15 (c), and brightest pixels, evaluated in the region of 100–255 (d). Different letters label statistical differences measured using the Tukey HSD test.

The all‐pairs comparison Tukey HSD test confirmed a statistically significant difference between baseline and sebum‐treated hair groups across all parameters. The cumulative and weighted counts for the darkest pixels decreased by 36% and 35%, respectively. By contrast, the changes in the brightest pixel region were much greater, with reductions of 61% and 64%, respectively, indicating that hair dulling was primarily caused by a loss of brightness rather than a reduction in hair darkness.

Meanwhile, hair brightness evaluation after serum application showed 142% and 160% improvement in cumulative and weighted counts, respectively, compared with a negative control. The improvement in cumulative and weighted counts for the darkest pixels reached 35% and 45%, respectively. The lack of statistical difference between the serum‐treated and baseline groups confirmed the restoration of hair vibrancy.

To conclude, the optimized imaging protocol using a 250 × 250 pixel ROI improved data quality by minimizing variability from tress morphology, while reducing the number of replicates required. The application of dust sebum emulsion consistently reduced hair shine parameters by 40%–60% as measured by shiny point count and percent area occupied by them. It also caused greying of the hair. The diminished brightness contributed to hair greying more than a reduction in the blackest pixels. Additionally, cumulative and weighted counts for bright and dark pixels offer robust metrics for assessing vibrancy, although further validation against consumer perceptions is recommended to confirm their relevance to real‐world hair appearance. Evaluation of on‐market shine serums on sebum‐dulled tresses demonstrated that restoring the dull hair shine is challenging without washing it. Only one of four products achieved improvements that exceeded the negative control and returned shine and colour vibrancy to baseline levels. These findings provide a comprehensive framework for evaluating shine and colour vibrancy in textured hair and support the development of effective hair care products.

Curl shrinkage evaluation

The method for assessing curl shrinkage is a modification of the established curl droop method, which has been employed at TRI Princeton for over a decade to evaluate curl retention and style longevity by measuring hair length as a function of time, RH and product used. The method adaptation was focused on evaluating conditions that are critical for assessing the shrinkage‐mitigating effects of hair care products.

Impact of humidity on shrinkage of textured hair

The primary factor influencing overall length retention, regardless of hair type, is RH under which the products must perform. To quantify the RH effects of humidity on curl elongation, the hair was treated with a product system consisting of shampoo, conditioner and curl cream, and allowed the hair to dry at 30%, 60% and 80% RH. The hair length behaviour of curl types 3 and 4 is presented in Figures 24 and 25, respectively.

FIGURE 24.

Change of type 3 hair curl length as a function of RH for product a system containing shampoo, conditioner and curl cream. Data are shown as mean ± standard error of the mean.

FIGURE 25.

Change of type 4 hair curl length as a function of humidity for product a system containing shampoo, conditioner and curl cream. Data are shown as mean ± standard error of the mean.

The hair shrinkage profiles in regimen‐treated type 3 hair showed RH dependence. At 30% and 60% RH, the initial slope was steep, with a pronounced inflection point leading to comparable equilibrated shrinkage of approximately 15%. At 80% RH, the slope was shallower compared with 30% and 60% RH, with an inflection greatly delayed and the final shrinkage at the beginning of the plateau being 15.8%. The statistical analysis of the change in length at the equilibrium point showed no difference in shrinkage levels of type 3 hair (Table 1).

TABLE 1.

JMP analysis for type 3 curl elongation as a function of RH for the product of a system containing shampoo, conditioner and curl cream.

Treatments	N	Mean	SD	SE of mean	Differences
60% RH	3	−14.7	0.3	0.2	A
30% RH	5	−15.1	2.6	1.2	A
80% RH	4	−15.8	0.5	0.3	A

Note: Levels not connected by the same letter are statistically different.

At 30% and 60% RH, the shrinkage profiles for type 4 hair (Figure 25) were more nuanced than those of type 3 hair (Figure 24). At 30% RH, curl length decreased the steepest for the first 2 h, plateauing at −7.4%. By contrast, the slope was shallower at 60%, with a broad inflection between 4 and 6 h. The hair exposed to 60% RH continued to shrink beyond the 30% RH plateau, reaching a slightly lower equilibrated value of −6.3%. The 80% RH shrinkage profile was broad, with undefined inflection, and the equilibrium was not reached.

Statistical analysis of the length change at the final time point revealed that hair exposed to 80% RH shrank less than hair exposed to 60% RH (Table 2). This discrepancy could be attributed to incomplete hair dryness at 80% RH.

TABLE 2.

JMP analysis for type 4 curl elongation as a function of RH for the product of a system containing shampoo, conditioner and curl cream.

Treatments	N	Mean	SD	SE of mean	Differences
80% RH	5	−5.0	0.6	0.3	A
30% RH	3	−6.3	0.3	0.2	A	B
60% RH	5	−7.4	1.6	0.7		B

Note: Levels not connected by the same letter are statistically different.

The observed differences in shrinkage profiles of two types of hair evaluated at 30% and 60% RH make it difficult to definitively attribute variations to inherent morphology, treatment‐fibre interactions or measurement variability. Nonetheless, the 80% RH condition presented challenges associated with the difficulty drying the hair during 9 h. This prolonged drying time poorly reflects real‐world consumer drying experiences; thus, 80% RH was excluded from acceptable conditions to test stationary textured hair.

30% and 60% RH conditions proved to yield meaningful results while allowing practical hair drying times. Selection of conditions within this range should be guided by the laboratory's ambient conditions or the target market climate. In this study, 60% RH was adopted as it is, on average, the closest to the conditions of our geographical region.

Impact of humidity on shrinkage of textured hair

To determine the appropriate test duration that accommodates various product uses, time experiments were conducted at 60% RH. Types 3 and 4 hair was treated with commercial product combinations, detailed in Figures 26 and 27, respectively. The statistical evaluation of treatment performances is presented in Tables 3 and 4, respectively.

FIGURE 26.

Change in curl length as a function of time for eight treatment regimens on type 3 hair. Data are shown as mean ± standard error of the mean.

FIGURE 27.

Change in curl length (Shrinkage) as a function of time for eight treatment regimens on type 4 hair. Data are shown as mean ± standard error of the mean.

TABLE 3.

JMP analysis for type 3 curl change in length as a function of treatments.

Treatment	Mean	SD	SE of mean	% Change compared with shampoo 1	Difference
Shampoo 1 + Gel 3 20% dosage	−7.9	0.6	0.3	−69	A
Shampoo 1 + Curl Cream 3	−8.5	1.0	0.4	−67	A
Shampoo 1 + Gel 3	−10.0	0.9	0.4	−60	A	B
Shampoo 1 + Gel 2	−10.6	1.3	0.6	−52	A	B
Shampoo 2 + Conditioner 2 + Curl Cream 2	−14.1	0.8	0.4	−48	A	B
Shampoo 1 + Conditioner 1 + Curl Cream 1	−14.7	0.3	0.2	−41		B
Shampoo 1 + Gel 1	−23.7	3.0	1.3				C
Shampoo 1	−27.6	5.1	2.3				C

Note: Levels not connected by the same letter are statistically different.

TABLE 4.

JMP analysis for type 4 curl change in length as a function of treatments.

Treatment	Mean	SD	SE of mean	% Change compared with shampoo 1	Difference
Shampoo 1 + Conditioner 1 + Curl Cream 1	−7.4	1.6	0.7	−65	A
Shampoo 2 + Conditioner 2 + Curl Cream 2	−7.6	0.8	0.4	−64	A	B
Shampoo 1 + Gel 3 20% dosage	−8.6	0.6	0.4	−59	A	B
Shampoo 1 + Curl Cream 3	−8.6	0.3	0.2	−59	A	B
Shampoo 1 + Gel 2	−9.3	0.5	0.3	−56		B
Shampoo 1 + Gel 1	−10.1	0.7	0.3	−52		B	C
Shampoo 1 + Gel 3	−12.9	1.0	0.4	−39			C
Shampoo 1	−21.0	1.6	0.7					D

Note: Levels not connected by the same letter are statistically different.

The type 3 hair curl shrinkage for the eight treatments can be grouped into the following behavioural trends (Figure 26):

• Minimal shrinkage group: Shampoo 1 + Gel 3 at 20% dosage and Shampoo 1 + Curl Cream 3 exhibited an initial shallow slope, with an inflection point after 2–3 h. Beyond this point, performance begins to plateau at approximately 8% shrinkage.

• Intermediate shrinkage group: Shampoo 1 + Gel 2 and Shampoo 1 + Gel 3 displayed a steeper initial slope than the first pair, with a similar inflection point at about 3 h, and plateauing at approximately the same shrinkage level, ranging from 10% to 10.6%. The Shampoo 1 + Gel 2 group had the most pronounced inflection point among all treatments studied, indicating the clearest drying or curing stage at 2 h.

• Higher shrinkage group: Shampoo 1 + Conditioner 1 + Curl Cream 1 system and the Shampoo 2 + Conditioner 2 + Curl Cream 2 system showed more pronounced shrinkage within the first hour, resulting in a steeper initial slope, followed by a more gradual and broad shrinkage profile without reaching a plateau until 4–6 h, at approximately −14.1% to −14.7%.

• Control‐like shrinkage group: Shampoo 1 and Shampoo 1 + Gel 1 exhibited similar shrinkage profiles without a significant difference determined between them at the end of the experiment.

The range of type 4 hair shrinkage (Figure 27) was narrower than that of type 3 hair, reflecting the morphological constraints between treated hair and baseline shrinkage. Six performance profiles overlapped more substantially. Ranked from least to greatest shrinkage, they are as follows: Shampoo 1 + Conditioner 1 + Curl Cream 1 < Shampoo 2 + Conditioner 2 + Curl Cream 2 < Shampoo 1 + Gel 3 (20% dosage) < Shampoo 1 + Curl Cream 3 < Shampoo 1 + Gel 2 < Shampoo 1 + Gel 1. This range spans from −7.4% to −10.1% shrinkage.

Within this set of treatments, Shampoo 1 + Conditioner 1 + Curl Cream 1, Shampoo 2 + Conditioner 2 + Curl Cream 2 and Shampoo 1 + Curl Cream 3 exhibited broad inflections in their shrinkage profiles around the 3 h mark and were statistically indistinguishable at the end of the experiment (Table 4). By contrast, the gel treatments in this set displayed slightly greater shrinkage and sharper inflections at approximately 2 h.

The inflection of Shampoo 1 + Gel 3 20% dosage also occurred approximately at 2 h, but the final shrinkage reached 12.9%.

Finally, the control (Shampoo 1 group) was statistically distinct from all other groups. It displayed a significant initial drop in curl length, followed by an inflection at 2.5–3 h, and then reached a plateau at 21%.

To conclude, type 3 hair demonstrated greater differentiation between tested treatments with more pronounced shrinkage profiles compared with type 4 hair, consistent with differences in morphology (looser coils in type 3 allowing more dynamic response to product effects). Experiments with various commercial products at 60% RH demonstrated that type 3 hair shrinkage can be evaluated over a 6 h drying period at 60% RH, while type 4 hair required 8 h to reach the equilibrium. The tested products demonstrated the capability to reduce shrinkage by up to 69% for type 4 hair and up to 65% for type 3 hair, with treatments incorporating fixatives (gels) or mechanisms that weigh fibres down (curl creams).

These results validate 60% RH as a practical and representative test condition for substantiating curl elongation or length‐retention claims in textured hair care products, while highlighting the need for curl‐type‐specific durations to ensure robust and reproducible outcomes.

Three‐point bending test

Including consumer‐relevant terms ‘flexibility’ or ‘absence of crunchiness’ in the claims substantiation portfolio for curl‐elongating treatments can increase market appeal. This is particularly useful when differentiating fixative‐containing formulations such as gels that are often perceived as producing stiff curls despite delivering excellent elongation and definition.

To quantify flexibility, the three‐point bending technique, commonly used in the industry for fixative testing [8], was adapted for textured hair evaluation. Results for representative treatments of type 4 hair are shown in Figure 28.

FIGURE 28.

Curl shrinkage was evaluated using image analysis, while curl flexibility was measured with the three‐point bending technique. Different letters indicate statistically significant differences. Red letters labels represent statistical differences in curl shrinkage among the treatments, while blue letters labels indicate statistical differences in hair flexibility across different treatments. Data are shown as mean ± standard error of the mean.

Gel 3 applied at 20% dosage achieved excellent shrinkage control (Table 4), while the energy required to bend the treated tress was very high, indicating significant stiffness. By contrast, Gel 1 and Curl Cream 3 showed comparable performance to Gel 3 in shrinkage control but maintained hair flexibility similar to that of untreated hair. These findings demonstrate that high‐performance elongation can be decoupled from undesirable stiffness, allowing formulators to balance definition with a more natural feel.

It is important to note that although McMullen and colleagues demonstrated a range of parameters that can be extracted from the force‐displacement curves when testing straight hair [8], the inherent curliness and variable geometry of textured hair limited reliable multi‐cycle analysis; therefore, reliable results are obtained only from a single hair bundle penetration. This limitation restricts the ability to assess treatment longevity.

Contact angle study

Hair damage evaluation

Contact angle measurements have long served as a sensitive indicator of hair surface wettability and damage. The present study adapted contact angle measurements, previously published by Zur Wiesche and colleagues [9], to evaluate their utility for differently treated coily hair and their potential use for claims substantiation studies.

Type 4 hair received three types of damage: heat damage, oxidative damage and exposure to very high alkalinity—relaxer damage. The dynamics of the contact angle of differently treated hair over a 6 s period are presented in Figure 29.

FIGURE 29.

The contact angle data as a function of treatments and water droplet time spent on a hair surface. Data are shown as mean ± standard error of the mean.

Upon initial contact with a water droplet and throughout the 6 s experiment, the contact angle of virgin control hair was statistically indistinguishable from that of blow‐dried and flat‐ironed hair (Figures 30 and 31).

FIGURE 30.

Contact angle of initial water droplet after contact with hair fibre for Virgin, Blow‐Dried, Flat‐Ironed, Bleached, Dyed and Relaxed Hair. The figure contains a representative water droplet at initial contact with the fibres for each group. Different letters label statistical differences measured using the Tukey HSD test.

FIGURE 31.

Contact angle of water droplet 6 s after contact with hair fibre for Virgin, Bleached, Blow‐Dried, Flat‐Ironed, Dyed and Relaxed Hair. The figure contains representative images of water droplet contact with the fibres at the 6 s time point. Different letters label statistical differences measured using the Tukey HSD test.

The initial contact angle (t = 0 s) between water and relaxed hair was not statistically different from that of virgin or bleached hair. At the 1 s time point, the angles of all damaged hair groups were significantly different from one another, with relaxed hair exhibiting the highest angle. By the end of the experiment (t = 6 s), the contact angle for the relaxed hair group remained higher than that of the oxidatively damaged hair groups, reaching an average value of 52°.

Tukey outlier removal was performed on the contact angle data for dyed hair. Three measurements were excluded as outliers. It was hypothesized that the water droplet did not absorb quickly into the hair due to uneven dye application. This inconsistency is likely attributed to the dye being applied to black hair, where visual confirmation of even product application was challenging.

Although bleaching is a significantly stronger oxidative treatment than dyeing, the present data indicate that surface hydrophobicity was affected in a remarkably similar manner. Dyed and bleached hair exhibited similar initial contact angles with water (Figure 30). The contact angle for dyed hair was higher than that of bleached hair only at the 1 s time point. At later time points, the angles of these treatment groups became statistically indistinguishable (Figure 31). The similarity may arise from shared mechanisms such as cuticle lift and oxidation of lipids and cystine, despite differences in the severity of internal fibre damage.

Contact angle comparison of hair damaged by relaxer before and after conditioning treatment

To demonstrate the suitability of the method for claims substantiation, a proof‐of‐principle study was conducted using relaxed hair and relaxed hair treated with a shampoo and conditioning regimen. The dynamics of the water contact angle for differently treated hair are shown in Figure 32. The statistical analysis results for the contact angles at 0 s and 6 s are presented in Figure 33.

FIGURE 32.

Contact angle data as a function of water droplet time spent on a hair surface for Virgin, Relaxed and Treated Relaxed Hair. Data are shown as mean ± standard error of the mean.

FIGURE 33.

Contact angle between water droplet and Virgin, Relaxed and Treated Relaxed Hair: (a) 0 s time point and (b) 6 s time point. Different letters label statistical differences measured using the Tukey HSD test.

At initial hair contact with a water droplet, the contact angles of the three treatment groups (virgin, relaxed and regimen‐treated relaxed hair) were not significantly different. After 1 s, however, the contact angle of relaxed hair decreased significantly compared to that of the virgin hair and regimen‐treated relaxed hair groups. Meanwhile, application of the conditioning regimen on relaxed hair successfully mitigated this shift, maintaining contact angle statistically similar to that of virgin hair throughout the 6 s experiment (Figure 33). This indicates that the applied product restored consumer‐perceived porosity (wettability and moisture management) to levels comparable with undamaged hair.

From published literature, contact angle measurements between hair bundles and water have been used to evaluate virgin, virgin delipidated and bleached hair [9, 10]. Schulze Zur Wiesche et al. noted that this method was only reliable for contact angles not lower than 80 degrees due to rapid sorption on a more damaged surface [9]. The refinement introduced here—high‐frame‐rate video recording, followed by frame‐by‐frame extraction and analysis, allowed reliable measurement of angles throughout the water sorption trajectory, even for highly absorbent, damaged hair. This improvement significantly expands the method's sensitivity and applicability to evaluate properties directly linked to consumer perception of hair porosity across a broader range of damage states, as well as its changes due to conditioning, bond‐repair or porosity‐balancing formulations.

CONCLUSION

Shine evaluation method

This study adapted an image‐based shine evaluation method for Walker type 4 hair testing, leveraging a defined ROI and parameters less sensitive to curl pattern and colour. This approach ensures accurate shine measurements across diverse hair types. Appropriate dosages of hair greying agents were established for creating reliable negative controls, simulating real‐world dulling conditions. The method revealed that hair greying primarily results from the loss of brightness in light reflection. It also demonstrated the effectiveness of shine treatments in restoring vibrancy by enhancing both the darkest and brightest shades. One of the tested textured hair serums showed a 122% increase in shine point count, a 175% increase in percent area occupied by reflections and full restoration of colour vibrancy. Findings prove the method's ability to differentiate product efficacy on textured hair.

Curl shrinkage test method

The standardized curl shrinkage test method, adapted for 30% and 60% RH, provided robust evaluations of curl elongation treatments. By tailoring test durations to 6 h for type 3 hair and 8 h for type 4 hair, the method accommodated differences in curl patterns. Additionally, reducing hair tress mass to 0.25 g improved drying efficiency and ensured accurate length evaluations for type 4 hair. These adaptations enabled differentiation of product performance, making the test method more practical and reliable for textured hair.

Three‐point bending technique

The adapted three‐point bending technique effectively assessed the trade‐off between shrinkage control and hair flexibility. It distinguished products that increased stiffness, such as Gel 3, from those that maintained flexibility while providing excellent shrinkage control, such as Gel 1 and Curl Cream 3. This method complements curl shrinkage test method by providing insights into the tactile properties that consumers will experience, offering a comprehensive analysis of treatment effects on textured hair.

Contact angle adaptation for textured hair

The development of an adapter for the goniometer enabled accurate measurement of contact angles as consumers perceived hair porosity in type 4 hair. This adaptation addressed the challenge of analysing coily hair, which previously lacked robust methods for such measurements. Results showed that heat, oxidants and relaxers induce damages that create three distinct surface hydrophobicity profiles. The surface hydrophobicity was preserved after blow drying and flat ironing, while relaxed hair displayed greater hydrophobicity than bleached hair after 2 s of water exposure. This method is also suitable for evaluating product efficacy in damaged textured hair, contributing to better product development for textured hair consumers.

Our research provides valuable tools for the cosmetic industry, enabling more inclusive and accurate assessment for a broader range of hair types.

FUNDING INFORMATION

Project sponsors of this study are given in alphabetical order: Aveda and Bumble and Bumble (Estee Lauder), BASF, Croda, L'Oréal, Lubrizol, Procter & Gamble, Symrise, Syensqo (joined the project as Solvay), Unilever and TRI Princeton. One sponsor wishes to remain anonymous.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Supporting information

Data S1.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.