Correlating facial skin parameters with age and gender in population of Shaanxi Province, China

This study was designed to comprehensively evaluate the changes in facial skin biophysical parameters with age, as well the influence of gender differences in populations of Shaanxi Province, China.


| INTRODUC TI ON
As the largest organ in the human, the skin covers the entire body and protects the various tissues and organs of the body from external aggression.The skin acts as a barrier in two ways: it prevents the loss of water, electrolytes, and other substances from the body, and it prevents the penetration of harmful substances from outside. 1 In addition to age and location, some skin parameters vary considerably between different ethnic groups such as Caucasians, Yellows, and Blacks.The yellow race is mainly found in the Asian region, but there are also internal differences due to climatic conditions and living habits in different regions.China has 34  The results of studies of skin surface pH, SCH, and sebum content in people of different sexes and ages have been inconclusive, partly because of small sample sizes. 2 In addition, skin physiological parameters such as TEWL, SCH, sebum content, and skin elasticity can be influenced by geographical region, ethnicity, age group, gender, and occupation.Aging reduces the ability of the stratum corneum to synthesize sebum, which affects the homeostasis of the stratum corneum and even disrupts the skin barrier. 3,4veral studies have demonstrated that TEWL is the most commonly used parameter to assess skin barrier function, with higher TEWL being associated with skin barrier damage and lower TEWL being associated with healthy skin, and a recent meta-analysis indicates that TEWL appears to be generally similar or reduced in older people compared to younger people. 5SCH and sebum content decrease with age. 6However, it has also been suggested that there is no significant correlation between TEWL and SCH and age. 7With age, there is an increase in blood flow, skin redness index (a*) and wrinkle severity, 8,9 but other studies have shown that skin redness index (a*) decreases with age. 10 Several studies have proven that women produce less estrogen after the menopause, which leads to a decrease in skin elasticity, which means skin elasticity may be negatively correlated with age. 11,12e affects all skin parameters and gender is also an important factor in skin parameters.Skin thickness is significantly greater in men than women, 13 but skin elasticity is not greatly different between the sexes. 14Some studies have found that there may also be differences in sebum production, surface pH, and melanin between male and female skin, 15 for example, men produce more sebum than women, women's skin surface pH is higher than men's, and men have higher melanin content than women, that is, men's skin is darker, etc.There is no cosmetic product specifically designed for the Northwest China population, so by collecting facial skin parameters from the Shaanxi population and exploring the effects of different genders and age groups on the skin physiology of the Shaanxi population in China, we aim to provide better daily skin care or design a specialized cosmetic product for the Northwest China population, especially the Shaanxi population, to cope with the unique skin condition of the Chinese population.

| Subject characteristics
The study was conducted in accordance with the tenets of the Declaration of Helsinki, and all subjects signed an informed consent form.A total of 481 subjects aged 18-65 years (mean 34.11 ± 12.50 SD) participated in the study, of whom 114 were males aged 18-60 years (mean 28.84 ± 12.10 SD), and 367 were females aged 19-65 years (mean 35.74 ± 12.19 SD).Specific information on the gender and age of the subjects is shown in Table 1.
The exclusion criteria were as follows.
(1) Individuals who have had an anti-inflammatory medication applied to the test area within the last 2 months or who have a clinically unresolved inflammatory skin disease.(2) Patients with insulin-dependent diabetes or those with serious systemic health problems such as cancer.

TA B L E 1
(3) Patients with autoimmune diseases or those who have received anti-immune treatment within the previous 3 months.
(4) Women who are breastfeeding or who are pregnant.
(5) Individuals whose test results are affected by scarring, pigmentation, atrophy, bright red nevi, or other defects in the area to be tested.
(6) Persons with a high degree of physical sensitivity.(7) Those who are unable to complete the required elements of the test or who are otherwise deemed by the investigator to be unsuitable for participation in the test.

| Study design
The study was conducted in the spring, summer, and autumn of Shaanxi

| Statistics
Data were statistically analyzed by SPSS 26.0 software.
Spearman's rank test was used to verify the relationship between skin parameters and age.The strength of the correlation is judged according to the absolute value of the correlation coefficient R.
The specific rules are as follows: 0.00-0.

| Comparison of differences in skin parameters between different age groups
The subjects were divided into four age groups: 18-29 years,

| Relationship between skin parameters and age
The correlation between skin parameters and age was analyzed by Spearman rank test, as shown in Figure 2.Among the 14 skin parameters, the skin parameter R5 was weakly correlated (p < 0.01), R2, R7, and sebum were moderately correlated (p < 0.01), and wrinkle length was strongly correlated (p < 0.01).

| Gender differences in skin parameters
Gender differences in skin parameters are summarized in the box plot in Figure 3, and the specific data are collected in Table 4.
Compared with male, female had higher Scheme (p < 0.01), lower erythema (p < 0.01), higher skin smoothness (p < 0.01), lower wrinkle length (p < 0.01), and lower sebum (p < 0.01).In addition, there was no significant difference in melanin, R0, R2, R5, R7, F4, and pH between males and females, but as can be seen through Table 4, the mean values of melanin, R0, and F4 were lower, and the mean values of R2, R5, R7, pH, and skin redness index (a*) were higher in females compared to males.

| DISCUSS ION
At present, several articles have been published on facial skin characteristics and age and facial skin characteristics and gender in Chinese population, but there are few parameters involved. 17,18wever, most of the articles focused only on the skin status of women and ignored men, or detected fewer parameters, which did not allow for a comprehensive assessment of facial skin status.In this study, 14 skin parameters, including hydration, sebum content, skin surface pH, skin elasticity, wrinkles, skin smoothness, and skin color, were counted, and their effects on facial skin parameters were investigated in terms of age and gender, respectively.

| Skin parameters and age
In this study, we demonstrated that SCH and TEWL did not change significantly with age and had a weak correlation with age in the Shaanxi population (Figures 1 and 2).Several investigators have already found that SCH in the cheek area does not correlate strongly with age, whereas TEWL decreases significantly with age. 17,19This is somewhat different from our findings, but it may be a unique skin physiological parameter characteristic of the Shaanxi population.It is well known that higher TEWL indicates severe impairment of skin barrier function, and when TEWL decreases with age, it implies that the older the age, the better the skin barrier function may be. 5,10,20Some studies have suggested that the decrease in TEWL with age may be related to the increase in stratum corneum thickness with age. 6Although our results showed that TEWL did not significantly decrease with age, there was a tendency for TEWL to decrease.
Skin elasticity capacity, an important indicator of skin aging, was examined five parameters: R0, R2, R5, R7, and F4.Among them, R0, F4 all represent skin firmness, the smaller the value the better the skin firmness.R2 represents the total skin elasticity, R5 represents the proportion of net skin elasticity, and R7 represents the elastic recovery ability, the larger the value the better the skin elasticity.
There was no significant correlation between R0 and F4 with age, but R0 did not change significantly in the first three age groups and dropped abruptly in the 54-65 age group, while F4 did not change significantly in the 18-29, 30-41, and 54-65 age groups, and increased steeply in the 42-53 age group and was significantly different.The question of these two anomalies is not explained and requires further follow-up to call subjects for testing and conclusions.Some researchers have found that skin firmness is constant, independent of age. 21R2, R5, and R7 did not show a purely linear relationship (Figure 1), but there was a significant moderate correlation with age (Figure 2).Compared to the youngest group, R2, R5, and R7 all increased at 30-41 years and then significantly decreased, showing a highly significant difference in the oldest group (p < 0.01).This indicates that middle-aged women have higher skin elasticity than the younger group instead.This may be due to the fact that the skin condition of the population may still be in a normal state during this period, after which the components supporting skin elasticity begin to degrade with age as collagen in the skin decreases and the damaged elastic fiber network increases 22,23 as well as the accumulation of hazardous substances produced by prolonged exposure of the skin to ultraviolet rays, 24 which can lead to a drastic decrease in the elasticity of the skin.
Generally, skin smoothness is negatively correlated with age; however, our experimental results confirm that there is no significant correlation between this and age, which is the same as the known findings. 25However, wrinkles show a significant increase, with a strong correlation with age, 26 suggesting that there is no significant correlation between the smoothness of the skin and the amount of wrinkles.In addition, we found that sebum content, the most important component in maintaining skin barrier function, decreased rapidly with age, with a decrease of more than 70% in the oldest ancestors compared to the youngest group (Figure 1), and there was a significant moderate intensity correlation between sebum content and age (Figure 2, R = −0.504),which is consistent with the results of several other studies. 27,28The sebum content also affects the measurement of the pH value of the skin surface, in addition, the higher the moisture on the skin surface, the higher its pH value. 29There is evidence that skin pH increases with age, 27,30 which, contrary to our findings, may be due to a significant decrease in sebum content with age, which leads to a decrease in skin surface pH value.
Skin color depends mainly on erythema and melanin content.In this study, three parameters, erythema, melanin, and skin redness index a*, were examined in the hope of finding an association between skin color and age in the Shaanxi population.The results demonstrated that there was no significant correlation between either erythema, melanin, or a* and age, that is, there was no significant correlation between skin color and age; however, several studies have shown that skin color darkens significantly with age. 10,25is appears to be a large difference from our results, which leads to two ideas: either there may be some bias due to the small number of volunteers in our higher age group, which leads to no significant difference, or our results correctly reflect the characteristics of skin color in the Shaanxi population: skin color has no significant correlation with increasing age.

| Relationship between skin parameters and gender
The present study found that SCH was significantly lower in men, and TEWL was higher in women in the Shaanxi population (Figure 3, p < 0.01), which is consistent with the known facial skin characteristics of the Chinese population. 18This indicates that in China, women have better skin barrier function and higher skin water content compared to men.In addition, we found no significant differences in the parameters related to skin elasticity, R0, R2, R5, R7, and F4.However, through Table 4 we can find that the mean numbers of R0 and F4 parameters are higher in men than in women, and the mean numbers of R2, R5, and R7 parameters are smaller than in women, which indicates that although the difference in skin elasticity between the  two sexes is not significant, women may have slightly better skin elasticity compared to men. 18in gloss was higher in women than in men (p < 0.01), and a cohort study of a Chinese population reported that skin radiance correlated with facial location and gender, although their data indicated a significant difference only on the forehead. 18Our findings provide further evidence that there are equally significant differences in cheek skin radiance between the sexes.In addition, the results of this study showed that wrinkle length was greater in men than in women (p < 0.01), suggesting that men may be older than women in appearance.Also, a study has shown that smoking may lead to wrinkling and loss of skin elasticity, and that the number of men who smoke is much higher than that of women, which may also contribute to the lower skin elasticity and longer wrinkle lengths in men than in women. 31e sebum content was higher in men than in women (p < 0.01), and the finding consistent with other studies 27,30,32 One study suggested that the large difference in sebum content between the sexes may be due to differences in sex hormone particularly in men with high levels of dehydroepiandrosterone and active sebaceous glands producing sebum. 18However, this study found no significant difference in skin surface pH in women compared to men, but the mean pH value in men was smaller than that in women (Table 4).
Parameters related to skin color were examined for erythema levels, melanin levels, and a*.The results demonstrated that erythema levels were higher in males than in females (p < 0.01) and melanin levels were higher in males than in females, which means that men have darker skin color than women, which is the same as the results of published studies. 33,34I G U R E 2 Correlation of the parameters of the skin with age.The horizontal coordinate represents the age and the vertical coordinate represents the value of the parameter; a.u.for arbitrary unit.
Overall, gender has a greater impact on different parameters of facial skin, especially for men who embrace a worse skin condition than women, including but not limited to skin moisture content, skin elasticity, skin radiance, skin wrinkles, skin color, and more.This may be due to the fact that men pay less attention to skin care than women.

| Limitations
Firstly, this study was conducted in Shaanxi Province, which is representative of the facial skin characteristics of the population in Shaanxi Province, but not fully representative of the facial skin physiological characteristics of the population in Northwest China or China as a whole.Secondly, at the beginning of the study, we hoped to collect an equal number of volunteers from both genders.
However, during the volunteer screening process, although we tried to increase the number of male volunteers as much as possible, we found that the number of male volunteers was much lower than our expectation after we excluded those who did not meet the criteria of nerfing, which might lead to a low statistical efficiency in our data analysis.Finally, when we measured the parameters of the volunteers, we could not guarantee that all the skin parameters of the different provincial autonomous regions, they are in different geographical areas and have different dietary habits, which results in different skin characteristics for people in different parts of China.Shaanxi Province is the representative province of Northwest China, where you can observe the unique climate of the Northwest region and the influence of food habits on people.
Many previous studies have focused on the relationship between various skin parameters and age, gender, and body part, but studies of facial parameters in the Chinese population are relatively few or have a small number of subjects and no variability in the results.In this study, skin parameters were measured on 481 volunteers of different ages between 18 and 65 years, 114 males and 367 females, by using dermatometers equipped with different probes.The main skin parameters measured were SCH, TEWL, erythema, melanin, elasticity parameters (R0, R2, R5, R7, and F4), gloss, skin surface pH, skin redness index (a*), wrinkle length, sebum content, and their relationship with age and sex.
province, China, and measured from May to October, 2022.Volunteers were allowed to relax for 30 min in a room maintained at 22 ± 2°C and 50 ± 5% relative humidity after washing their faces with detergent.In this study, the Corneometer® CM 825 probe, the Tewameter® TM Hex probe, the Sebumeter® SM 815 probe, the Mexameter® MX 18 probe, the Cutometer® Dual MPA 580 probe, the Skin-PH Meter PH 905 probe, the Skin-Colorimeter Flex CL 440 probe, the Skin-Glossymeter GL 200 probe, and the Antera 3D Camera for Skin Analysis from Miravax Ireland Ltd were used to collect data on skin parameters.SCH was measured with the Corneometer® CM 825, which surveyed the change in dielectric constant due to hydration of the skin surface by changing the capacitance of a precision capacitor; TEWL was measured with the Tewameter® TM Hex, which gauged skin surface temperature and relative humidity; sebum was measured with the Sebumeter® SM 815, based on oil spot photometry; melanin content and erythema of the skin were measured with the Mexameter® MX 18, which surveyed the amount of absorption/reflection of three light waves by the skin; skin elasticity parameters R0, R2, R5, R7, and F4 were measured by the Cutometer® Dual MPA 580, which gauged the intensity of light waves as the skin recovered from mechanical deformation; skin surface pH was measured by the Skin pH Meter PH 905, which measured the skin surface H + concentration; skin redness index a* was measured using the Flex CL 440 colorimeter, which detected light reflected from the skin; gloss of skin was measured by measuring the reflection of light emitted from the skin with the Skin Glossimeter GL 200; skin wrinkle length was measured by the Antera 3D Camera for Skin Analysis to create a 3D model of the skin surface.

F I G U R E 1
Changes in skin parameters by age group.The left Y-axis with the bar graph represents the value of this parameter and the right Y-axis with the line graph represents the rate of change of the mean of the last three age groups compared to the youngest group; "*" for p < 0.05 and "**" for p < 0.01; a.u.for arbitrary unit.

F I G U R E 3
Differences in skin parameters between genders."*" for p < 0.05, "**" for p < 0.01; a.u.for arbitrary unit; a.u.for arbitrary unit.TA B L E 4Skin parameters between genders.
Table of subjects' information characteristics.

unit) 18-29 years 30-41 years 42-53 years 54-65 years Total
3 | RE SULTS3.1 | Subjects' informationA total of 481 subjects were screened for this study and due to the inconsistent schedules of the subjects, subjects did not measure the exact same parameters and no subject had all 14 facial Parameter (Note: a.u.for arbitrary unit.TA B L E 2 Number of subjects with different parameters.skinparametersmeasured.SCH was measured by 481 subjects, TEWL by 481 subjects, erythema by 196 subjects, melanin by 64 subjects, R0, F4, R5 by 127 subjects, R2 by 157 subjects, R7 by 96 subjects, gloss by 93 subjects, pH by 226 subjects, redness a* by 192 subjects, wrinkle length by 91 subjects, and sebum by 160 subjects.Details of the number of subjects for each parameter are given in Table2.
Summary of data on skin parameters for different age groups.The data represent mean ± SEM of different facial skin parameters in four age groups; the skin redness index a * was not analyzed in the 43-54 years age group because there was only one subject.a.u.for arbitrary unit.
TA B L E 3

Parameter (unit) Male Female Mean ± SEM N Mean ± SEM N
Note: a.u.for arbitrary unit; N represents the number of subjects involved in the measurement of each parameter.