Methods adapted to evaluate products for textured hair: Combing force and breakage

Abstract

Objective

To demonstrate the ability of adapted or developed test methods to quantify friction and breakage in textured hair.

Methods

Walker type 4 hair was used for illustrations. The modified Garcia & Diaz's wet friction method was used to evaluate hair combability and product ability to reduce the combing forces. Hair breakage was evaluated using both a conventional dry tensile test and a repeated combing test method that had been developed for type 4 textured hair. Both the number of broken fibres and the percentage of prematurely broken fibres were used to assess treatment efficacy in reducing breakage.

Results

Wet friction method: The proposed method adaptations include recommendations for substrate preparation, combing 16 times while rewetting hair every 5 times and evaluating maximum force instead of area under the curve. The benchmarking study showed products' ability to reduce hair friction by 50%–60%, with antipollution treatments performing comparably to those suggested for textured hair. We have also demonstrated that the natural oils do not reduce hair friction despite reducing breakage due to combing. The repeated wet combing method filled the gap experienced by the industry using repeated grooming techniques. We proposed grooming treated coily hair tresses in a wet state (manually) using a comb for a total of 100 strokes, rewetting every 20 passes. The evaluation of broken fibres showed reduced breakage after the use of conditioning and lubricating treatments (by 38%–64%), with silicone oil providing the greatest reduction (72%) and confirming the method's sensitivity. Tensile testing demonstrated high textured hair prevalence for premature breakage, which linearly depends on the water content in the hair. The study examining different treatment layering methods suggested that it is possible to sufficiently coat wet textured hair to reduce water migration out of the hair, as indicated by Young's modulus evaluation. It also showed that correctly managing premature breakage via plasticizing hair can outweigh the break stress reduction observed in healthy hydrated fibres.

Conclusions

The examined methods are shown to be appropriate to evaluate both the manageability and breakage of naturally curly hair, as well as test products' ability to improve these properties.

We adapted and refined methods to assess friction and breakage in Walker Type 4 hair, enabling sensitive benchmarking of conditioning and lubricating treatments. These tests revealed that effective products significantly improve manageability and reduce breakage, providing consumer‐relevant data to support performance claims for textured hair.

INTRODUCTION

Hair serves a dual role as both a protective barrier for the skin against environmental elements and a medium for personal identity and expression. Its structure is broadly categorized into the inner cortex and the outer protective cuticle layer. The cortex is composed of structural proteins responsible for the hair's mass, strength and elasticity. The cuticle consists of tightly packed, overlapping layers that protect the cortex from damage and environmental stressors.

Regular grooming, such as combing or brushing, helps to maintain hair alignment but can also cause cuticle damage due to friction and tangling. Environmental stressors, such as UV exposure, may alter the hair's lipid layer, resulting in changes to fibre–fibre interactions [1]. Garcia and Diaz defined ‘combability’ as the subjective ease of combing, influenced by the mechanical forces encountered along the hair shaft [2]. Hair products like conditioners and oils are commonly used to improve hair manageability.

The combing method is a standard claims substantiation test widely employed in our laboratories to quantitatively evaluate the combability of hair products on mainly straight and wavy hair types. First proposed by Garcia and Diaz, the method involves pulling a hair tress from its root end through a comb attached to a force‐measuring device (Instron Tensile Tester) at a constant defined speed. This arrangement generates data showing the load (in grams) opposing or generated by the combing process relative to the comb's position along the tress [2].

Robbins and Reich explored the relationship between fibre curvature and combing behaviour, performing a wet combing test on 10‐inch kinky hair purchased from Black panellists. The kinky tresses were soaked in tap water for 10 min, rinsed under running tap water and combed 20 times while water continued to flow through the tress. The tresses were then attached to the Instron load cell and pulled through three times, measuring the forces generated by the comb [3]. Kinky tresses belong to the hair sub‐category of textured hair fibres, characterized by a distinct, tightly coiled structure that leads to frequent tangling and greater susceptibility to grooming‐related damage. Visual and perceptive methods have been used by L'Oreal to compare styling aids on textured hair by combing in the wet state to evaluate curl evenness and definition [4]. However, instrumental evaluation of hair products on textured hair using wet combing remains less understood and standardized for claims substantiation [5].

The increased curvature of textured hair fibres makes them more prone to wrapping around each other, leading to easier tangling compared with straight or wavy hair. Consequently, consumers are advised to comb textured hair in a wet state to enhance flexibility and reduce combing forces [6, 7]. Wide‐tooth combs and a bottom‐up detangling approach are recommended to minimize excessive force, scalp discomfort and long detangling times. High‐lubrication products, such as detangling gels and high‐molecular‐weight masks, further improve manageability by reducing friction. Improved combability, often referred to as ‘detangling’, is therefore highly desired by consumers with textured hair. There is a clear consumer demand to understand how hair products can be formulated to improve the combability of textured hair.

Strong hair is often desirable because it is perceived to associate with continuous growth, enhance overall hair condition and allow greater styling versatility. This perception aligns with the psychosocial value placed on long, healthy hair in many cultures, where it is associated with beauty, vitality and personal identity. While these values shape public perception, understanding hair's structural integrity requires precise scientific evaluation.

Physical wear, such as abrasion from repeated combing, snags or chemical treatments, can weaken hair structure, eventually leading to breakage under stress. Several tests are suitable for evaluating such damage and assessing the efficacy of hair care treatments. The fatigue test, which subjects hair fibres to repeated cycles of mechanical stress until failure, simulates the wear experienced during daily grooming and is most frequently used to evaluate damages to the hair [8]. The most consumer‐relevant repeated grooming test involves combing or brushing hair tresses repeatedly for a desired number of cycles and counting the number of broken hairs [9]. It is mainly used for claims substantiation purposes of products designed for less curly hair. Another method, the tensile test, measures hair's resistance to breakage by extending individual fibres using a Tensile Tester until they break, providing data on (i) break stress, (ii) Young's modulus (flexibility) and (iii) break extension [10] amongst other parameters. These methods have been well‐studied and standardized for different hair types and their damage.

African‐descendant hair demonstrates higher levels of breakage, validated by mechanical testing. Its continuous twists create stress concentrations along the fibre [11]. Single‐fibre tensile studies show a decrease in break stress as curliness increases [12]. Kamath et al. found that textured hair is more susceptible to premature breakage [11]. Other research reflects how grooming practices, like braiding, can seriously influence the structural integrity of textured hair. Molamodi et al. demonstrated that frequent braiding reduced the cross‐sectional area, break stress and break extension of textured hair compared with occasional braiding [13]. Epps and Wolfram observed that water content in hair influences combing forces and breakage. Lower grooming forces were noted for wet, highly coiled African hair compared with its dry state, whereas the opposite was true for wavy‐to‐straight Caucasian hair [14]. Another study showed that using protein treatments on relaxed coily hair reduced premature breakage [15].

This study aimed to adapt commonly used hair mechanical testing methods so they could be applied reliably to highly textured hair. Three complementary approaches were explored: Wet combing measurements to evaluate friction and detangling performance, repeated combing to assess grooming‐related breakage and tensile testing to examine premature fibre failure. Together, these methods provide a framework for evaluating the performance of products designed for textured hair.

MATERIALS AND METHODS

Substrate

Single‐source, Walker Type 4 virgin was procured from TSEBO Manufacturing and Technical Services (Johannesburg, South Africa). For the wet combing study and wet repeated combing studies, 0.5 g and 0.25 g tresses were bound, respectively. The hair length was approximately 12 cm.

For all the studies, we used commercially available products. The ingredients are listed in the Supporting Information S1.

Hair treatments

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

We used the following product dosages and treatment protocols:

Shampoo: 0.4 mL/g hair.

Application: Wet hair for 30s, apply shampoo dosage, massage through the entire tress for 30s, rinse.

Conditioner/Mask: 0.4 mL/g hair.

Application: Wet hair for 30s, apply conditioner dosage, massage through the entire tress for 30s, rinse.

Leave‐in Products (including oils): 0.15 mL/g.

Application: Wet hair for 30s, apply leave‐in dosage, massage through the entire tress for 30s.

Test methods

Wet combing

Instron 5500R (Instron Corporation, Norwood, MA, US) was modified in‐house to accommodate the comb setup (Figure 1).

FIGURE 1.

Experimental setup for hair length evaluation.

The treated 0.5 g wet hair tress was pre‐combed using a wide‐tooth comb (with >5 mm spacing between teeth), secured in the grippers and pulled through the comb while the load cell measured the forces. Each tress was combed 16 times, with rewetting after every 5 passes. Rewetting was conducted by lightly misting the hair with water after every five combing passes, spraying three times on each side from a distance of six inches to maintain consistent moisture levels. The amount of water in a wet tress after pre‐combing was approximately 120% of the dry hair weight. During combing over five strokes, about 30% of this water was lost. The spray bottle should be selected to deliver an amount of water equivalent to the loss during combing, thereby restoring the tress's water content to the pre‐combing level.

Four replicates per group were used in this study when the following steps are taken:

Data were acquired and analysed using Bluehill software (Instron Corporation, Norwood, MA, US). The maximum force and area under the curve parameters were extracted. Outlier analysis was performed to evaluate each treatment group. Replicates identified as outliers were removed and replaced with newly measured tresses. The difference between the treatment and control groups was calculated using the equation below:

$$\text{Change in force}=\left(\frac{\text{force of treatment group}}{\text{force of control group}}-1\right)\times 100$$

Repeated combing

Treated 0.25 g tresses were manually groomed in a wet state using a 0.5 mm comb (Figure 2) for a total of 100 strokes, with rewetting after every 20 passes. To ensure visibility, the combing of the hair was performed over a white surface. Fibres were collected and assessed after the final combing stroke. Four replicates per group were used in this study. Outlier analysis was performed to evaluate each treatment group. Replicates identified as outliers were removed and replaced with newly measured tresses.

FIGURE 2.

Comb used for repeated grooming test.

Tensile testing

Fibres were mounted on brass crimps and equilibrated overnight at 40%, 60% or 80% relative humidity. Dimensional measurements were conducted under the same environmental conditions using a laser scanning micrometre (FDAS770 Fibre Dimensional Analysis System, Diastron Ltd., UK). At least 50 replicates per treatment group were measured at five locations. The cross‐sectional area was calculated using UVWin 4.3.0.77 software (Diastron Ltd., UK).

Fibre breakage testing was performed using an MTT690 Miniature Tensile Tester (Diastron Ltd., UK) by extending the fibres at a 40 mm/min rate. The fibres that broke at the crimp were removed from the data pool. Young's modulus was determined by analysing the linear slope of the stress–strain curve within the 0.2%–1% extension range after removing signs of decrimping. The number of prematurely breaking fibres was determined by counting the fibres that broke below 10% strain.

Statistical analysis

Wet combing and repeated grooming data were evaluated as follows:

The Tukey Quartile Method data analysis was used to identify:

• To test the results of 16 strokes until no outliers were left in the data set.

• To test the average results of 4 tress replicates. In case outlier was found, the average result of this tress is removed and a new tress was tested to replace the removed data point.

By testing four replicates and using additional hair to replace outliers, we sought to improve the sustainability of resources.

To find an outlier, the following steps are carried out:

Find the upper quartile (Q3) – 75% of data points are lower than this observation.

Find the lower quartile (Q1) – 25% of data points are lower than this observation.

Calculate the gap between the quartiles (interquartile ranges): IQR = Q3–Q1.

A value lower than Q1 – 1.5 × IQR or higher than Q3 + 1.5 × IQR in its respective group is considered an outlier.

JMP analytical software (SAS Institute Inc., 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 < 0.05 were considered statistically significant and are indicated in the graphs using different letters for statistically different groups.

Pearson's chi‐squared test was performed in Excel software (Microsoft, Redmond, WA, US). Null hypothesis (H₀): The observed differences in premature breakage are independent of the treatments. The null hypothesis is rejected if the p‐value from the chi‐squared test is <0.05.

RESULTS AND DISCUSSION

Wet combing

The objective of this work was to adapt the conventional wet combing method, so it could reliably evaluate detangling performance in highly textured hair.

Sample preparation considerations

The primary technical function of most conditioning products is to lubricate the hair surface. This lubrication makes hair more manageable, better aligned and less prone to tangling. Our study aimed to adapt the method initially proposed by Garcia & Diaz [2] for straight hair combing and validate products specifically formulated for textured hair. We proposed several changes to the original methodology:

• Reduced tress size and appropriate comb selection: We used smaller amounts of hair for tress binding to conserve hair resources. This necessitated selecting a comb that could accommodate the reduced tress size. Through trial and error, we identified a comb capable of generating a maximum frictional force exceeding 100 gF.

• Increased number of combing strokes: It is a natural propensity for Textured hair to tangle, thus providing greater variability between measurements. To improve data reliability, we increased the number of combing strokes to 16. Moreover, we used Tukey outlier analysis to identify and exclude them before calculating averages and conducting further statistical analyses.

To reduce variability in data, we also suggest the following recommendations for binding and handling textured tresses

• Managing bushy tresses: If the tress is too bushy to fit within the length of the comb teeth, bind the top of the bundle with a rubber band, then split the tress in half and bind each half with additional rubber bands. This flattens the tress, allowing it to pass through the comb more effectively.

• Ensuring consistent curl tightness: Before binding, ensure that the tresses have similar curl tightness. Even hair from the same donor can show visible differences in curl patterns, which may significantly affect combing results and skew product evaluation.

• Pre‐Combing after washing: Pre‐comb the tress using a wide‐tooth comb (with >5 mm spacing between teeth) before testing. This step helps remove tangles that could otherwise cause excessive force during detangling, potentially pulling out hair chunks or overloading the load cell.

• Rehydrating the hair.

• We found that using a comb with teeth spaced 3 mm apart, rounded individual teeth with a diameter of 1.5 mm, provides good resolution for both tighter and looser Type 4 hair curls.

• Gentle handling and comb pattern removal: Handle the tresses gently and remove any set comb patterns by lightly massaging the hair near the binding (as shown in Figure 3). Running a tress with a pre‐set comb pattern through the test setup can reduce combing forces and increase variability within the 16‐stroke results.

FIGURE 3.

Tress massage area while ‘deleting’ the comb pattern.

If these recommendations are not followed, it is recommended to increase the number of replicates significantly, and this may require the use of non‐parametric data analysis.

Considerations for substrate uniformity

The substrate uniformity was explored to improve the reproducibility of results. Walker Type 4 hair was obtained in random‐length and mass bundles. To understand if there is a difference between panellists with similarly looking curl tightness, we investigated two conditions: single‐source hair with a total length of 12 cm and a mix of hair from two sources (12 cm and 14 cm). The 12 cm hair was weighed and bound into 0.5 g tresses without additional preparation. The 14 cm hair was trimmed to 12 cm, mixed in a 1:1 ratio with the 12 cm hair from the other panellist and then tied into tresses. Approximately 1 cm of the total hair length was allocated for binding. The combing results for tresses from different sources are shown in Figure 4.

FIGURE 4.

The maximum combing force (A) and area under the curve (B) of hair from different sources. Different letters label statistical differences measured using Student's t‐test.

The combing force of single‐source hair was 10% higher than that of two‐source hair, and the difference was statistically significant. Statistical analysis did not reveal a difference between the hair groups when the area under the curve was used for friction evaluation, suggesting that maximum combing force might be a more sensitive parameter.

We postulate that, despite the hair having similar curl patterns, the trimming of the tips may have contributed to the observed differences. This stresses the importance of blending hair from multiple panellists in equal proportions, as the individual hair history is unknown.

Conditioning product testing

For this study, we evaluated five formulations or sets of formulations using Type 4 hair. Consumers with textured hair often brush or comb their hair in the shower while conditioning treatments are still applied. To replicate this behaviour, we investigated the friction of hair treated with three rinse‐off regimens, testing it immediately after treatment. The tresses were then rinsed for 30 s and tested again. In the second part of the study, we included a regimen containing a leave‐in treatment for comparison.

The results are presented in Figures 5 and 6.

FIGURE 5.

The maximum combing force (A) and area under the curve (B) of hair treated with rinse‐off products. The measurement was performed immediately after the conditioning treatment application. Different letters label statistical differences measured using the Tukey HSD test.

FIGURE 6.

The maximum combing force of hair treated with rinse‐off and leave‐in products. The measurement was performed after rinsing rinse‐off products. Different letters label statistical differences measured using the Tukey HSD test.

These results show more than a two‐fold reduction in combing force compared with negative control (non‐conditioning shampoo) and a slightly lower but comparable reduction in area under the curve when tresses are combed with rinse‐off conditioning treatments on the hair. The statistical differentiation of four product groups was more favourable for benchmarking when maximum combing force data were used. Therefore, we continued our analysis using only this parameter.

When measured in their intended modes of application—rinse‐off products rinsed and leave‐in products left on the hair—the conditioning treatments significantly reduced the combing force of coily hair. Interestingly, the maximum combing force for the ‘leave‐in’ regimen is 46% higher than that of the worst‐performing ‘rinse‐off’ regimen.

The comparison of combing forces for rinse‐off conditioning treatments before and after rinsing within individual regimens showed a slight trend of increasing forces, although this difference was statistically insignificant. We used rinse‐off products at a 40% dosage; therefore, the relatively low increase in forces after a 30‐s rinse was unexpected. We postulate that this outcome results from the product being effectively ‘massaged’ onto the hair by the comb during the 16 cycles of testing (approximately 10 min per tress). This finding provides valuable insight for consumers: When conditioning products are evenly applied to the hair surface, they adhere well enough to minimize detangling loss during rinsing.

This study also demonstrated that antipollution treatments designed for all hair types can be as effective in detangling coily hair fibres as treatments specifically formulated for textured hair.

Hair oils testing

Natural and synthetic oils have long been essential in the care and maintenance of textured hair, providing benefits specifically tailored to the needs of curly and coily hair types. Textured hair tends to be naturally prone to dryness, which consumers often associate with issues like frizz, tangles and breakage. Oils serve as both a sealant and a nourishing treatment, helping to address these challenges effectively. To investigate the oil effect on hair combability, we tested the following commercially available oils applied on non‐conditioning shampoo‐washed hair:

• Seed, Fruit and Nut Oils 1

• Seed, Fruit and Nut Oils 2

• Seed, Fruit and Nut Oils 3

• Seed and Essential Oils

• Seed, Nut, Fruit and Essential Oils

• Silicone Oil

The results are presented in Figure 7.

FIGURE 7.

The maximum combing force of hair treated with oils. Different letters label statistical differences measured using Tukey HSD test.

To many, this may come as a surprise, but none of the natural oils improved hair combability in a wet state. The mixture of Seed, Fruit and Nut Oils 1 and a mixture of Seed and Essential Oils performed the best in a sense that increased the frictional forces insignificantly compared with shampoo‐washed hair. The rest of the oils increased maximum combing forces significantly:

• Seed, Fruit and Nut Oils 2 – 31%.

• Seed, Fruit and Nut Oils 3 – 53%.

• Seed, Nut, Fruit and Essential Oils – 70%.

There is a strong trend showing that silicone oil reduced combing forces, although the whole data set evaluation led to this reduction being statistically insignificant.

Fregonesi and colleagues [16] studied Brazilian oils for their ability to improve various hair properties (unknown ethnicity). Their study showed that wet hair combability is improved with the use of natural and mineral oils, while butters negatively affected the detangling of the hair. The major components in our tested oils were seed and fruit oils. Therefore, our results are the opposite of what Brazilian researchers published. To explain our results, we postulate natural oils form a relatively thick, hydrophobic barrier on the hair surface, which possibly traps water, creating an oil–water interface that increases the drag and surface friction when combing wet hair. Natural oils may not spread as evenly as silicones and result in uneven coverage, increasing localized friction during combing, which could explain why silicone oil performed better.

To conclude, this study proposes a tailored testing protocol for textured hair and provides valuable insights into product performance and consumer relevance. Rinse‐off and leave‐in conditioning treatments significantly reduced combing forces, tested natural oils did not improve wet hair combability and some significantly increased frictional forces, while silicone oil showed a trend toward reducing combing forces, though not statistically significant. The maximum combing force was identified as a more sensitive parameter for analysis.

Repeated combing for breakage evaluation

Repeated grooming experiments are typically conducted on straight and wavy hair in a dry, controlled state using commercially available or custom‐built devices. For hair in relatively good condition hair (including bleached), more than a thousand strokes are often required to generate a reasonable number of broken ends [8].

Walker Type 4 hair, known for its resistance to combing, presents unique challenges. While various grooming methodologies for textured hair have been discussed in blogs [6, 7], no published methodology specifically addresses repeated grooming testing for coily hair. Furthermore, since consumers with coily hair typically avoid brushing their hair in a dry state [6, 7], adapting a dry repeated combing device for wet combing poses significant challenges. Practical issues such as wet hair adhering to random surfaces instead of falling into the collection tray enormously complicate the adaptation process. Considering consumer behaviour and the problems associated with automation, we opted for manual wet combing as the basis for generating broken ends.

Sample preparation and testing insights

Walker Type 4 hair was prepared in‐house by binding 0.25 g tresses with rubber bands. Hair morphology and tress shape variation were controlled in the same manner as in the wet combing experiment, and care was taken to ensure that no loose hair strands were present. A 12 cm extended hair length provided sufficient volume for testing. Although not typically used by consumers, a ‘rat‐tail’ comb was found suitable for combing these small tresses. Historical repeated grooming experiments on straight or wavy hair indicated that at least 50 broken fibres in a negative control were necessary for adequate test resolution. Given the manual nature of this test, we aimed to limit the number of strokes to 100.

However, for some type 4 panellists' hair, particularly hair attributed to type 4A or hair that was freshly trimmed, 100 comb strokes may not produce the required number of broken ends. To address the occasional problem of overly healthy hair, we tested several pre‐damaging methods, including bleaching, heat exposure, UV exposure and mechanical damage. The quickest and most effective method for worsening hair quality was dry brushing. Using a comb with 2 mm spacing between teeth, 50 cycles of dry combing successfully predamaged the hair for testing (1 mm comb removed an excessive amount of hair). Due to the infrequent occurrence of very low‐damage hair and the natural variability of hair substrates, it is difficult to determine whether controlled pre‐damaging contributes significantly to the observed variation.

It is important to note that operator‐dependent variability may be introduced while performing the manual repeated grooming procedure. Factors such as attention during tress preparation, combing force and stroke speed can influence the absolute values obtained. Because the tresses are relatively short, it is also difficult to precisely control stroke timing during manual grooming. To minimize variability, it is recommended that a single trained operator prepare all tresses and perform the entire test.

Product benchmarking

To understand wet repeated combing suitability for product benchmarking, we tested hair treated with the same products as listed in Figure 6. The results are presented in Figure 8.

FIGURE 8.

The broken ends of hair treated with rinse‐off and leave‐in products. Different letters label statistical differences measured using Tukey HSD test.

The data from testing coily hair after 100 wet grooming cycles show that all treatments statistically reduced breakage compared with the negative control (non‐conditioning shampoo group). The breakage of Textured Hair with both Rinse‐Off Regimens 1 and 2 is indistinguishable and lower by 38% and 48%, respectively, compared with the negative control. The Antipollution Regimen and Leave‐In Regimen delivered comparable results, with the number of broken fibres in these groups reduced by 64%. The correlation coefficient between breakage and friction results was 0.69, which indicates that the reduction in friction was important but not the only factor responsible for the decrease in breakage.

The poor oil performance in reducing fibre combability piqued our interest, and we tested them using repeated combing tests. The results are displayed in Figure 9.

FIGURE 9.

The broken ends of hair treated with commercially available natural and synthetic oil mixtures. Different letters label statistical differences measured using Tukey HSD test.

All natural oils, except for the combined mixture of Seed, Nut, Fruit and Essential Oils, improved fibre resistance to breakage by 33%–50%. Since commercially available oils include ingredient lists without specified concentrations, it is not possible to postulate why some were more effective than others. A parametric study is recommended to explore different types of oils and their impact on coily hair breakage (beyond the scope of this study).

Despite growing consumer aversion to silicone oil, it remains the most effective antibreakage treatment, achieving a 72% reduction.

To explain the result of this study, we postulate that although the interaction between natural oils, water and hair created uneven friction, leading to increased combing forces and making it more difficult to separate fibres, the clumping of hair may have helped prevent tangles and knots, thus reducing breakage. By contrast, silicone oil reduced combing forces slightly, but lubrication possibly enhanced this effect, resulting in the best performance in reducing hair breakage.

Textured hair breakage insights from tensile testing

Highly textured hair exhibits a pronounced elliptical shape and twists, introducing greater internal stresses within its cortex. Maintaining adequate hydration helps alleviate these stresses. Recognizing this need, consumers with textured hair have intuitively developed LOC and LCO methods, layering leave‐in conditioner (low viscosity), oil and cream (high viscosity conditioner) to retain internal moisture [17]. We sought to validate these routines using tensile testing under controlled laboratory conditions, evaluating whether these widely adopted practices can reduce water migration—often described by consumers as ‘sealing the hair surface’—and thus minimize breakage.

To visualize the relationship between hair water content and premature breakage, we prepared three sets of fibres to establish a calibration curve correlating humidity with premature breakage. The results are presented below.

Although only three points were evaluated, the results in Figure 10 suggest a strong linear trend (Pearson's correlation coefficient = 0.999) between hair water content and premature breakage within the tested region. After product application and overnight equilibration at 40% relative humidity, fibres treated using the LOC and LCO methods showed significantly reduced premature breakage compared with the control. Pearson's chi‐squared test revealed p‐values of 0.002 for the LOC group and 0.006 for the LCO group, indicating it is highly unlikely these reductions occurred by chance. Evaluating premature fibre breakage is not a new concept and has been discussed previously [4, 17]. However, the limited number of proof‐of‐principle studies, especially those involving statistical evaluations, has prevented this method from gaining wider industry recognition. These findings hopefully will encourage the use of premature fibre breakage assessment as a mechanical testing tool for generating novel product claims.

FIGURE 10.

Hydration and treatments' impact on internal hair properties. Premature breakage evaluated at 10% extension. Water content in hair was recalculated from data obtained via a dynamic sorption experiment.

Based on the calibration curve, one might assume that the water content in the LCO and LOC groups could reach levels corresponding to 75% and 78% relative humidity. However, the Young's modulus evaluation in Figure 11 shows that LCO‐ and LOC‐treated samples are statistically indistinguishable from samples at 60% RH. This finding implies higher water content compared with 40% RH but also suggests additional product effects beyond merely limiting water loss.

FIGURE 11.

Young's modulus of differently treated fibres. Different letters label statistical differences measured using Tukey HSD test.

Meanwhile, statistical analysis of the conventional breakage evaluation parameter, break stress, shows that, despite higher water content in the fibres, the average break stress across LOC and LCO samples remains comparable to that observed at 40% and 60% relative humidity. In fact, the absolute average values are slightly higher than those of the 40% RH control (Figure 12A). This finding is unexpected since fibres with higher water content would typically exhibit lower break stresses, thus could cast doubt on the water mitigation hypothesis. The stress–strain curve in Figure 12B indicates a shift toward lower break stresses in the LOC group. However, there is also a notable subset of prematurely broken fibres at 40% RH that are not present in LOC data, suggesting these fibres broke at higher stresses, effectively raising the average break stress for the LOC fibres.

FIGURE 12.

(A) Break stress of differently treated fibres. Different letters label statistical differences measured using Tukey HSD test. (B) Stress–strain curve comparing LOC group versus control at 40% RH.

Literature indicates that the force required to break hair is generally much higher than the force needed to pull the hair out of the follicle (except in cases of severely damaged hair) [18]. Wyness and colleagues evaluated hair pluckability in individuals of European and African descent, reporting a range of 24–68 g, although they did not specify the growth stage of the plucked fibres [19]. Berthiaume et al. reported 30–35 g for African hair and 60–65 g for European hair [18, 20], while Muthuvel and colleagues tested 30 Indian volunteers of both genders, finding an average plucking force of 87 g for anagen hair and 54 g for telogen hair, with variation depending on the scalp location [21].

In this study, the average force required to break fibres that did not exhibit premature breakage at 40% relative humidity (RH) was 65 ± 13 g (mean ± standard deviation), while fibres that broke before 10% extension required only 36 ± 8 g. Although premature breakage evaluation appears to be a promising parameter for simulating consumer‐relevant breakage through mechanical testing, a separate study involving textured hair panellists is needed to confirm that premature breakage indeed occurs at forces comparable to or lower than the hair plucking forces reported in previous studies.

CONCLUSION

We adapted and refined Garcia & Diaz's [2] wet combing method to evaluate the effects of conditioning products and oils on Walker Type 4 hair, emphasizing tress preparation, handling and testing conditions to ensure reproducibility and relevance. We proposed increasing the number of combing strokes, ensuring consistent rehydration and managing tress binding to reliably measure combing forces while focusing on the maximum force rather than the area under the curve. Benchmarking studies demonstrated that effective conditioning agents can reduce Walker Type 4 hair friction by 50%–60%, with antipollution treatments designed for all hair types performing comparably to those formulated for textured hair. By contrast, natural oils did not improve wet combability, with most formulations notably increasing frictional forces.

We also developed a repeated wet combing method to evaluate breakage in coily hair, addressing challenges posed by consumers' avoidance of dry brushing. With consistently prepared 0.25 g tresses at least 12 cm in length and employing a rat‐tail comb, this method produced reliable broken‐fibre counts, enabling product performance benchmarking. To address ‘overly healthy’ substrates, we introduced a pre‐damaging step—combing the hair 50 times in a dry state with a comb with 2 mm tooth spacing. Benchmarking showed 38–64% reduced breakage after using conditioning and lubricating treatments, with silicone oil providing the greatest reduction (72%), thus confirming the method's sensitivity.

The study examining layering treatments' effectiveness in reducing Walker type 4 hair breakage highlighted the tensile test suitability for substantiating product claims. Besides the conventional evaluations of Young's modulus and break stress, we propose statistically examining premature breakage in highly textured hair. Assessing premature breakage as an additional parameter offers heightened sensitivity for detecting consumer‐relevant damage, thereby strengthening product efficacy claims. Nonetheless, further research involving textured hair panellists is required to confirm that premature breakage occurs at forces comparable with or lower than hair plucking in real‐world scenarios.

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

None.

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.