Abstract
Background
Age‐related changes in scalp parameters affect hair quality and scalp condition. However, detailed data on biophysical parameters of the scalp across age groups remain scarce. We aimed to investigate the differences in scalp parameters between individuals in their 20s and 50s and analyze their sex‐specific variations.
Materials and methods
Two hundred participants (160 women and 40 men) were equally divided into 20s and 50s age groups. Biophysical parameters of the scalp, including elasticity, pH, trans‐epidermal water loss (TEWL), sebum production, desquamation, firmness, redness, and yellowness, were measured in the vertex, occipital, and temporal regions. Hair density and thickness were measured in the temporal region. The accumulation of advanced glycation end products (AGEs) in the skin was noninvasively measured in a subset of 60 women.
Results
Skin firmness and redness increased with age in women, whereas yellowness increased with age in both sexes. Sebum production and pH levels were significantly lower in the 50s age group than in the 20s age group, particularly in women. TEWL was lower in men in their 50s than in those in their 20s, particularly in the occipital region. A significant reduction in hair density was observed in the 50s age group in both sexes. AGE accumulation in the skin increased with age and was correlated with scalp skin yellowness.
Conclusion
Age‐related changes in scalp parameters have important implications for hair health and scalp condition. These findings emphasize the importance of considering age and sex when developing hair care strategies.
Keywords: advanced glycation end product, age, biophysical parameter, hair care, scalp, skin aging
1. INTRODUCTION
The complex phenomenon of skin aging is influenced by multiple factors, including both intrinsic chronological elements and environmental influences, such as exposure to ultraviolet radiation (UVR) and hormonal shifts. These combined elements contribute to the degradation of the structural integrity and functional capabilities of the skin. 1 Manifestations of the skin aging process include wrinkles, irregular pigmentation, skin dryness, and a reduction in dermal and epidermal thickness. 2 Numerous studies have reported age‐related changes in the epidermis and dermis. In vitro investigations have shed light on the consistent exposure of the skin to low‐grade inflammatory changes caused by external (e.g., UVR) and internal factors, leading to cellular senescence. 3
The aging process of the scalp follows similar principles to that of the skin, albeit with some natural protection from UVR, depending on hair density. 4 However, compared to the skin, clinical changes in scalp conditions with age have not been extensively examined, except for a well‐documented decrease in hair density and hair thickness. Recent studies have explored the utility of noninvasive tools in distinguishing a range of mechanical and functional skin parameters across different skin sites. One study included parameters such as trans‐epidermal water loss (TEWL), pH (acidity), erythema, stratum corneum hydration, skin stiffness, and elasticity in 15 healthy volunteers. 5 The results revealed significant differences in skin properties across different locations, demonstrating the potential of noninvasive techniques to consistently track changes in skin health over time.
Ongoing research efforts have attempted to elucidate age‐related variations in noninvasive parameters. Magnetic resonance imaging had been utilized to noninvasively analyze anatomical changes in the scalp and hair follicles in androgenetic alopecia and alopecia areata. 6 , 7 A previous study sought to construct a facial map based on six biophysical parameters in 20 volunteers, aged 24−83 years. 1 When the participants were divided into groups with mean ages in their 30s and 70s, the younger group displayed significantly higher TEWL and stratum corneum hydration, while exhibiting lower pH levels. The secretion of sebum was location‐dependent. Another study involving 500 healthy volunteers measured a range of biophysical parameters of the scalp, forehead, forearms, and legs. The older age group exhibited lower TEWL and hydration, whereas sebum production was elevated across all the measured anatomical sites. 8 However, detailed data on biophysical parameters of the scalp across age groups remain scarce.
Considering this knowledge gap, we aimed to provide additional information on the biophysical parameters specific to the scalp of the Asian population, with a particular focus on age‐related differences. We sought to contribute to the limited body of knowledge on scalp health and its variations with age, which could have profound implications for our understanding of overall skin health.
2. MATERIALS AND METHODS
2.1. Participants and study design
In this cross‐sectional investigation, we measured and compared various biophysical scalp parameters among two distinct age groups: 100 participants in their 20s and 100 participants in their 50s. We employed screening questionnaires and physical examinations to exclude individuals with active scalp skin conditions, such as seborrheic dermatitis, psoriasis, or eczema. Additionally, individuals who had taken medications or undergone phototherapy for scalp‐related problems within the month preceding the study were excluded. We also excluded those who had received any skin treatments or procedures (e.g., scalp scaling, Botox, fillers, laser therapy, or tattooing) within 3 months prior to the study. The institutional review board of our institution approved this study (approval number: GIRB‐20720‐OQ), and all participants provided written informed consent before participating in the study.
2.2. Measurements
All participants underwent a one‐time assessment of their scalp's biophysical properties. They were instructed to refrain from using hair or scalp products for 12 h before the examination. Measurements were conducted by a well‐trained and experienced investigator under standardized conditions at a controlled temperature of 20−24°C and a relative humidity of 45%−55%. Participants were required to acclimate to the climate‐controlled room for at least 20 min before the examination. Scalp biophysical parameters were measured using appropriate devices. The units of measurement and interpretation for each parameter are listed in Table 1. Skin elasticity (alpha value), firmness (penetration depth, mm), pH, desquamation (Desquamation Index, %), TEWL (g/m2h), sebum output (μg/cm2), redness (R, artificial unit), and yellowness (Y, artificial unit) were measured in the vertex, occipital, and temporal regions. For hair density and thickness, a 0.5 cm2 area of hair was sampled from the temporal region, and images were captured at 15× magnification using the Folliscope 5.0 (LeadM Corp., Korea). Hair density was determined by counting the number of hairs within a 0.5 cm2 circle centered on the measured area, and the value was converted to the number of hairs per 1 cm2. Hair thickness was measured by randomly selecting five hairs within the area, and the average thickness of these five hairs was recorded. Additionally, we noninvasively measured the accumulation of advanced glycation end products (AGEs) in the skin of a subset of 60 female participants to examine their relationship with scalp redness and yellowness. Participants with cardiovascular disease, type 1 and/or 2 diabetes, or a history of gestational diabetes were excluded from this subset. Skin autofluorescence was measured from approximately 4 cm2 of skin surface on the volar side of both forearms, serving as an estimation of AGEs accumulation in the skin (AGE reader, Diagnoptics Technologies, Netherlands).
TABLE 1.
Scalp biophysical parameters.
| Parameters | Measurement devices | Unit of measurement and interpretation |
|---|---|---|
| Skin elasticity | Ballistometer (BLS780, Pia‐Stron, United Kingdom) |
Alpha As the skin elasticity improves, the alpha value decreases |
| Skin firmness | Indentometer IDM800 (Courage & Khazaka, Cologne, Germany) |
Penetration depth (mm) As the skin firmness increases, the penetration depth decreases |
| Skin pH | Skin pH meter PH905 (Courage & Khazaka) | pH (expressed with one decimal) |
| TEWL | Tewameter Nano TMnano (Courage & Khazaka) |
g/m2h As the skin barrier function improves, the TEWL decreases |
| Sebum output | Sebumeter SM815 (Courage & Khazaka) |
μg/cm2 As the sebum output increases, the measurement increases |
| Skin desquamation | Visioscan VC98 (Courage & Khazaka) |
DI (Desquamation Index, %) As the skin desquamation increases, the DI increases |
| Redness | Scalp images obtained and analyzed by 60× polarized light device (ASW 300, PSIPLUS, Korea) |
R (red; AU) As the redness increases, the measurement increases |
| Yellowness | Scalp images obtained and analyzed by 60× polarized light device (ASW 300, PSIPLUS) |
Y = 1/B (B, blue; artificial unit) As the yellowness increases, the measurement increases |
| Hair density | Folliscope 5.0 (Lead M, Korea) |
N/cm 2 As the hair density increases, the measurement increases |
| Hair thickness | Folliscope 5.0 (Lead M) |
mm As the hair thickness increases, the measurement increases |
Note: The unit of measurements and its interpretations were derived from previous studies.
Abbreviations: AU, artificial unit; TEWL, transepidermal water loss.
2.3. Statistical analyses
Data are presented as numbers (percentages) or means ± standard deviations. The normality of the data was assessed using the Shapiro–Wilk test. Depending on the results, either the independent t‐test (parametric method) or the Mann–Whitney U test (nonparametric method) was employed to compare the measurements between the 20s and 50s age groups. Statistical analyses were conducted using SPSS version 25.0 (IBM corp. Armonk, NY, USA). Differences were considered statistically significant at p < 0.05.
3. RESULTS
3.1. Study participants
A total of 200 participants (160 women and 40 men) were included in this study. The mean age of participants in their 20s was 24 years, while those in their 50s had a mean age of 54 years. Scalp biophysical parameters between the 20s and 50s age groups were compared separately for women (Table 2A) and men (Table 2B). A comparison of hair density and scalp thickness according to age groups is shown in Table 3. Representative scalp images of each age group are shown in Figure 1, and summaries of changes in scalp parameters with increasing age for each sex are depicted in Figure 2.
TABLE 2A.
Comparison of biophysical parameters of the scalp, according to age group (women, N = 160).
| Vertex region | Occipital region | Temporal region | ||||
|---|---|---|---|---|---|---|
| Scalp index | 20s (N = 80) | 50s (N = 80) | 20s (N = 80) | 50s (N = 80) | 20s (N = 80) | 50s (N = 80) |
| Elasticity (Alpha) | 0.052 ± 0.010 | 0.050 ± 0.013 | 0.058 ± 0.013 | 0.055 ± 0.014 | 0.063 ± 0.010 | 0.062 ± 0.010 |
| p‐Value | 0.10 | 0.08 | 0.36 | |||
| Firmness (mm) | 1.10 ± 0.26 | 0.96 ± 0.27 | 1.34 ± 0.28 | 1.23 ± 0.27 | 1.27 ± 0.27 | 1.14 ± 0.29 |
| p ‐Value | 0.001 ## | 0.009 ## | <0.001 ### | |||
| pH | 5.03 ± 0.53 | 4.82 ± 0.52 | 4.80 ± 0.55 | 4.67 ± 0.48 | 4.88 ± 0.54 | 4.71 ± 0.49 |
| p ‐Value | 0.014 * | 0.12 | 0.007 ## | |||
| TEWL (g/m2h) | 28.2 ± 7.97 | 26.6 ± 6.86 | 31.5 ± 17.4 | 27.8 ± 8.91 | 30.6 ± 15.2 | 27.7 ± 8.21 |
| p ‐Value | 0.26 | 0.23 | 0.16 | |||
| Sebum (μg/cm2) | 73.8 ± 58.2 | 38.8 ± 32.5 | 64.9 ± 53.2 | 35.6 ± 40.3 | 54.1 ± 49.4 | 34.7 ± 40.2 |
| p ‐Value | <0.001 *** | <0.001 *** | <0.001 ### | |||
| Skin desquamation (%) | 6.95 ± 2.59 | 7.04 ± 2.76 | 6.66 ± 2.97 | 6.34 ± 2.87 | 7.67 ± 2.96 | 6.48 ± 3.24 |
| p ‐Value | 0.903 | 0.57 | <0.001 ### | |||
| Redness (R, AU) | 125.2 ± 13.4 | 135.4 ± 15.4 | 124.2 ± 15.5 | 133.6 ± 15.7 | 124.0 ± 15.4 | 137.2 ± 16.9 |
| p ‐Value | <0.001*** | <0.001 ### | <0.001 ### | |||
| Yellowness (Y, AU) | 41.9 ± 3.24 | 47.8 ± 5.40 | 40.5 ± 1.72 | 44.9 ± 4.18 | 41.3 ± 2.05 | 47.2 ± 4.31 |
| p ‐Value | <0.001 ### | <0.001 ### | <0.001 ### | |||
p‐Value < 0.05 independent t‐test.
** p‐Value < 0.01 independent t‐test.
p‐Value < 0.001 independent t‐test.
p‐Value < 0.05 Mann–Whitney U test.
p‐Value < 0.01 Mann–Whitney U test.
p‐Value < 0.001 Mann–Whitney U test.
Abbreviations: AU, artificial unit; TEWL, transepidermal water loss.
TABLE 2B.
Comparison of biophysical parameters of the scalp, according to age group (men, N = 40).
| Vertex region | Occipital region | Temporal region | ||||
|---|---|---|---|---|---|---|
| Scalp index | 20s (N = 20) | 50s (N = 20) | 20s (N = 20) | 50s (N = 20) | 20s (N = 20) | 50s (N = 20) |
| Elasticity (Alpha) | 0.055 ± 0.013 | 0.050 ± 0.010 | 0.058 ± 0.014 | 0.062 ± 0.011 | 0.070 ± 0.020 | 0.060 ± 0.010 |
| p‐Value | 0.39 | 0.45 | 0.09 | |||
| Firmness (mm) | 1.00 ± 0.26 | 1.07 ± 0.29 | 1.27 ± 0.26 | 1.34 ± 0.35 | 1.14 ± 0.30 | 1.22 ± 0.31 |
| p ‐Value | 0.40 | 0.48 | 0.23 | |||
| pH | 4.95 ± 0.49 | 4.88 ± 0.59 | 4.42 ± 4.45 | 4.61 ± 0.70 | 4.48 ± 0.44 | 4.64 ± 0.47 |
| p ‐Value | 0.73 | 0.32 | 0.25 | |||
| TEWL (g/m2h) | 25.7 ± 6.53 | 26.3 ± 7.65 | 34.5 ± 10.5 | 31.7 ± 21.3 | 32.7 ± 8.61 | 32.0 ± 13.37 |
| p ‐Value | 0.49 | 0.025 # | 0.25 | |||
| Sebum (μg/cm2) | 68.3 ± 51.0 | 79.1 ± 54.1 | 72.4 ± 78.9 | 62.9 ± 26.1 | 69.4 ± 57.1 | 61.2 ± 54.8 |
| p ‐Value | 0.39 | 0.36 | 0.71 | |||
| Skin desquamation (%) | 6.95 ± 2.46 | 6.32 ± 2.20 | 6.33 ± 2.60 | 5.13 ± 1.78 | 6.50 ± 2.82 | 5.79 ± 1.77 |
| p ‐Value | 0.47 | 0.19 | 0.29 | |||
| Redness (R, AU) | 140.4 ± 18.8 | 152.3 ± 24.3 | 133.9 ± 16.9 | 145.3 ± 19.0 | 138.6 ± 18.1 | 137.2 ± 15.7 |
| p ‐Value | 0.12 | 0.07 | 0.99 | |||
| Yellowness (Y, AU) | 42.2 ± 2.90 | 47.7 ± 5.17 | 40.7 ± 2.07 | 47.0 ± 6.66 | 41.7 ± 2.58 | 45.3 ± 4.51 |
| p ‐Value | 0.001 ## | <0.001 ### | <0.005 ### | |||
p‐Value < 0.05 independent t‐test.
p‐Value < 0.01 independent t‐test.
p‐Value < 0.001 independent t‐test.
p‐Value < 0.05 Mann–Whitney U test.
p‐Value < 0.01 Mann–Whitney U test.
p‐Value < 0.001 Mann–Whitney U test.
Abbreviations: AU, artificial unit; TEWL, transepidermal water loss.
TABLE 3.
Comparison of hair density and thickness of the scalp, according to age group.
| Hair index | Female (N = 160) | Male (N = 40) | ||
|---|---|---|---|---|
| 20s (N = 80) | 50s (N = 80) | 20s (N = 20) | 50s (N = 20) | |
| Hair density (N/cm2) | 157.00 ± 37.91 | 140.64 ± 28.85 | 160.73 ± 35.62 | 136.60 ± 21.06 |
| p‐Value | 0.004 ## | 0.015 * | ||
| Hair thickness (mm) | 0.10 ± 0.01 | 0.09 ± 0.01 | 0.09 ± 0.01 | 0.09 ± 0.01 |
| p ‐Value | 0.010 * | 0.206 | ||
p‐Value < 0.05 independent t‐test.
p‐Value < 0.01 independent t‐test.
* p‐Value < 0.001 independent t‐test.
p‐Value < 0.05 Mann–Whitney U test.
p‐Value < 0.01 Mann–Whitney U test.
p‐Value < 0.001 Mann–Whitney U test.
FIGURE 1.
Representative scalp images obtained using a 60× polarized light device.
FIGURE 2.
Summary of difference in scalp parameters with increase in age among males and females.
3.2. Scalp biophysical parameters
Among women, significant differences were observed between the 20s and 50s age groups in terms of firmness, sebum output, and yellowness across all scalp regions. The 50s age group exhibited increased skin firmness (lower mm values) (p < 0.01) and decreased sebum output levels (p < 0.001) in all regions than did the 20s age group. Additionally, the 50s age group had significantly lower pH values in the vertex and temporal regions (p = 0.014 and 0.007, respectively). Furthermore, the 50s age group exhibited significantly higher levels of redness (p < 0.001) and yellowness in all scalp regions (p < 0.001). However, no consistent patterns were found in skin elasticity, desquamation, or TEWL between the two age groups in women (Table 2a).
Among men, the 50s age group showed lower TEWL in the occipital region (p = 0.025) and elevated levels of yellowness in all regions (p < 0.001) than did the 20s age group. No significant differences were found in other parameters such as elasticity, firmness, pH, sebum output, skin desquamation, and redness level between the age groups among men (Table 2B).
3.3. Hair density and thickness
A significant decrease in hair density was observed in the 50s age group in both sexes compared to that in the 20s age group. In women, hair density decreased from 157.00 ± 37.91 N/cm2 in the 20s age group to 140.64 ± 28.85 N/cm2 in the 50s age group (p = 0.004). In men, hair density decreased from 160.73 ± 35.62 N/cm2 to 136.60 ± 21.06 N/cm2 (p = 0.015). Regarding hair thickness, a significant decrease was observed in women in their 50s (0.10 ± 0.01 mm) compared to those in their 20s (0.09 ± 0.01 mm) (p = 0.010). However, there was no significant difference in hair thickness between age groups in men (p = 0.206).
3.4. AGEs in the skin
In a subset of 60 female participants, AGE accumulation in the skin significantly increased with age, and this trend was consistent on both the left and right sides of the volar forearm (Table 4). The average AGE value for the 20s group was 1.98 ± 0.20, while the average for the 50s group was significantly higher at 2.58 ± 0.41 (p < 0.001). Furthermore, a notable positive correlation was found between scalp skin yellowness and skin AGEs in bivariate correlation analysis (r = 0.341, p = 0.008). However, there was no significant correlation between scalp redness and AGE levels in the skin (r = 0.097, p = 0.463).
TABLE 4.
Comparison of advanced glycation end products (AGEs) in skin, according to age group.
| Index | Female (N = 60) | |||||
|---|---|---|---|---|---|---|
| Left side | Right side | Average (left + right) | ||||
| 20s (N = 30) | 50s (N = 30) | 20s (N = 30) | 50s (N = 30) | 20s (N = 60) | 50s (N = 60) | |
| AGEs | 1.96 + 0.21 | 2.53 + 0.43 | 2.00 + 0.20 | 2.63 + 0.39 | 1.98 + 0.20 | 2.58 + 0.41 |
| p‐Value | <0.001 *** | <0.001 *** | <0.001 *** | |||
p‐Value < 0.05 independent t‐test.
p‐Value < 0.01 independent t‐test.
p‐Value < 0.001 independent t‐test.
4. DISCUSSION
The investigation of noninvasive biophysical parameters for the scalp is essential for advancing the field of scalp cosmeceuticals and deepening our understanding of healthy scalp and hair conditions. This enhanced understanding not only drives innovations in scalp and hair care products but also enhances their therapeutic effectiveness and aesthetic value, while accentuating the distinct biology of the scalp across various age and sex groups. In this study, we conducted a comprehensive investigation of scalp biophysical parameters across different age groups, revealing significant differences between individuals in their 20s and 50s. These findings highlight the complex and dynamic nature of skin aging and the physiological changes that occur within the scalp as a result of aging.
In our examination of sex‐specific changes, we found that women in their 50s exhibited increased skin firmness, yellowness, and redness, while sebum output decreased across all scalp regions compared with that of women in their 20s. These differences may be attributed to age‐associated sebaceous gland dysfunction, leading to drier and firmer skin with reduced oiliness. Additionally, decreased functional stem cell capacity, which is associated with aging, may contribute to increased scalp redness. Notably, older participants displayed lower pH values in the vertex and temporal regions, indicating an age‐associated adjustment in the acidic mantle of the skin.
Previous research 9 has highlighted the crucial role of appropriate sebum secretion in the development of a sensitive scalp, noting significant differences in sebum secretion between prediagnosed sensitive scalps and normal scalps, particularly in the occipital region. This disparity influences scalp microbiota and potentially contributes to scalp sensitivity. Another study 1 identified age and regional variations in facial sebum, with older individuals exhibiting altered sebum secretion in different regions. Our results are consistent with these findings, indicating a reduction in sebum secretion in older participants, which could potentially disrupt the normal scalp microbiota.
While a few studies have focused on skin pH in terms of regional variations and age‐related differences, 1 , 10 , 11 they have reported either no difference in pH or higher pH in older age groups in facial anatomical regions such as the forehead and cheeks. However, in this study, we observed lower scalp pH values in the older age group than in the younger age group. This difference may be attributed to the fact that those in the older group in our study were in their 50s, whereas previous studies had older age groups with an average age in their 70s. Previous studies have also shown that sun‐exposed skin contains more melanocytes, and the dendrites of melanocytes tend to be more acidic, resulting in a lower pH. 8 , 12 , 13 Therefore, the lower pH observed in the older age group may be a result of pigment accumulation due to chronic sun exposure. Overall, changes in sebum secretion and pH in the aging scalp could influence scalp microbiota and susceptibility to various scalp conditions, further emphasizing the role of age in modifying scalp conditions.
Among male participants, the differences in biophysical parameters were less pronounced. Older men exhibited lower TEWL in the occipital region and increased yellowness across all regions. This suggests that aging may affect the scalp barrier function differently in men and women, possibly because of variations in hair distribution, hair care practices, or hormonal differences. Although some studies have suggested no significant correlation between TEWL and age, 1 , 14 others have reported a decrease in TEWL with age, potentially owing to a positive correlation between TEWL and skin hydration. 8 However, there were no significant variations in other parameters, such as elasticity, firmness, pH, sebum output, desquamation, and redness levels between age groups in men.
We observed a significant correlation between age and the accumulation of AGEs in the skin, which may manifest as increased skin yellowness. A previous study has identified significant associations between AGEs and age, melanin level, and erythema as positive predictors. 15 We also observed a remarkable positive correlation between scalp skin yellowness and skin AGEs in bivariate correlation analysis, further emphasizing the intricate relationship between the biological aging process and alterations in scalp biophysical parameters.
Overall, we observed a significant reduction in hair density in both women and men in their 50s compared to that in younger participants. Moreover, women in the older age group experienced a considerable decrease in hair thickness in the temporal area than did those in their 20s, suggesting that hair thickness in women is influenced not only by hormonal changes during aging, as shown in men. This substantial decrease in hair density and thickness may provide valuable insights for the development of personalized scalp care and therapeutic strategies based on age and sex.
Nonetheless, this study has several limitations. First, it focused solely on two age groups (the 20s and 50s), limiting the generalizability of the findings to other age groups. Second, the imbalanced sex distribution (160 women and 40 men) may have influenced sex‐specific analyses. Third, owing to the technical constraints of the measurement device, we could not directly measure skin AGEs on the scalp. Third, the cross‐sectional design only provides a snapshot of the differences between age groups at a specific point in time, rather than portraying how scalp parameters evolve over time, as would be demonstrated in a longitudinal study. Lastly, our study does not account for potential confounding factors such as lifestyle, diet, or hair care habits, which may influence the observed differences in scalp parameters between age groups. Despite these limitations, our findings contribute to the existing body of evidence by shedding light on the diverse effects of aging on scalp health. Future longitudinal studies may provide further insights into the temporal changes in scalp biophysical parameters and the association between aging and environmental factors.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.
ETHICS STATEMENT
This study complied with the principles of the Declaration of Helsinki, Korean Good Clinical Practice guidelines, and local regulatory requirements. The study protocols and informed consent forms were approved by the Institutional Review Board of the Global Medical Research Center (IRB No. GIRB‐20720‐OQ). All the participants provided written informed consent.
Lee YI, Kim J, Park SR, et al. Age‐related changes in scalp biophysical parameters: A comparative analysis of the 20s and 50s age groups. Skin Res Technol. 2023;29:e13433. 10.1111/srt.13433
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available upon request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
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Associated Data
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Data Availability Statement
The data that support the findings of this study are available upon request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.