[Physiological Characteristics of the Facial Skin in Ethnic Tibetan Population Living at High Altitudes]

To investigate the characteristics of skin physiological parameters in ethnic Tibetan population living at ultra-high (4700 m) and high (3650 m) altitudes on the Xizang Plateau.

Using a multi-stage cluster random sampling method, this study measured facial skin parameters related to the skin barrier system such as sebum secretion (SM), skin pH (pH), corneum moisture content (CM), and transepidermal water loss (TEWL), as well as melanin-related parameters such as erythema (E), melanin (M), individual typology angle (ITA), lightness (L), red-green chromaticity (a value, a), and yellow-blue chromaticity (b value, b) in ethnic Tibetans living at ultra-high (average altitude: 4700 m) and high (average altitude: 3650 m) altitudes. The control group primarily measured the skin parameters of unexposed areas (neck) in the high-altitude population, serving as the baseline reference values for skin parameters.

A total of 627 participants were enrolled, including 164 from ultra-high-altitude regions and 257 from high-altitude regions (128 males and 293 females; average age [48.03 ± 13.39] years), as well as 206 controls (72 males and 134 females; average age [48.67 ± 12.50] years). Other physiological indicators were mostly within normal ranges. Comparison of parameters showed that, compared with the high-altitude population, the ultra-high-altitude population showed significantly higher E value (P < 0.01), TEWL value (P < 0.001), and M value (P < 0.001), but lower CM, ITA, and L values (P < 0.001). There were no significant age-stratified differences, though age-related variation trends were observed. Gender differences showed that males had higher a, M, and TEWL values than females (P < 0.001), but lower ITA and L values (P < 0.001). In ultra-high-altitude areas, males had lower b value than females (P < 0.001), while in high-altitude areas, males showed higher E value (P < 0.001) and lower SM and pH values than females. These differences narrowed with increasing altitude. Ultra-high-altitude males had higher TEWL (P < 0.001) and M values (P < 0.05), but lower E, ITA, L, and b values (P < 0.01) than high-altitude males. Ultra-high-altitude females demonstrated higher TEWL, E, M, and b values, but lower CM, ITA, and L values compared with high-altitude females (P < 0.001), with statistically significant differences. Linear, correlation, and phenotypic network analyses showed that pH, CM, TEWL, ITA and L values were linearly correlated with altitude. The b values of both males and females showed a linear relationship with altitude, and the M value of females was linearly correlated with altitude. Significant correlations were observed among parameters, with strong positive correlations between E and a and between ITA and L, and strong negative correlations between value of M and ITA, M and L, and a and b. The network structure demonstrated good centrality and stability, with E, M, ITA, and a value as key nodes. PCA analysis revealed significant overall differences in skin parameters among Tibetan population at different altitudes, with distinct clustering characteristics. The main factors influencing classification were SM, CM, pH, E, TEWL, and b values.

There are significant differences in skin parameters between ethnic Tibetan population at ultra-high and high altitudes on the Xizang Plateau. Altitude, gender, and age affect skin parameters, particularly those related to changes in the skin barrier system and melanin-related skin structures.