Comparisons between Caucasian-validated photo-numeric scales and Korean-validated photo-numeric scales for photo-ageing. Insights from the Singapore/Malaysia cross-sectional genetics epidemiology study (SMCGES) cohort.

Background: Photo-ageing is a form of skin ageing which affects the entire face. A photo-aged skin has a diverse variety of wrinkles and dyspigmentation all over the face. Here, we discuss photo-ageing on the Chinese skin evaluated using a photo-numeric scale developed and validated on Caucasian skin (i.e., Caucasian scale) and evaluated using a photo-numeric scale developed and validated on Korean skin (i.e., Korean scale). The Korean scale can be subdivided into two scales that separately address the wrinkling and dyspigmentation constituents of photo-ageing.

Aim: As there are currently no photo-ageing scales for Chinese skin, the main objective of this study is to adapt existing photo-ageing photo-numeric scales for use on ethnic Chinese skin.

Method: Three trained assessors studied facial photo-ageing on 1,081 ethnic Chinese young adults from the Singapore/Malaysia Cross-sectional Genetics Epidemiology Study (SMCGES) cohort.

Results: All assessors are highly internally consistent (Weighted Kappa (κ) values≥0.952). We found that the Caucasian scale and Korean scale give nearly synonymous results for the wrinkling constituent of photo-ageing (R = 0.9386). The two scales are strongly concordant (Spearman's Rank Correlation (ρ) value: 0.62 ± 0.06, p = 1.31×10). A weak-to-moderate inter-scalar level of agreement (Cohen's Kappa (κ) values: 0.38 ± 0.05, p = 8.87×10) persists and is statistically significant after accounting for agreements due to chance. When tested on ethnic Chinese skin, both scales detect photo-ageing consistently (Area under curve [AUC] values: 0.76-0.84). Additionally, the Korean scale for the dyspigmentation constituent of photo-ageing is concordant with both the Caucasian scale (R = 0.7888) and the Korean scale for the wrinkling constituent of photo-ageing (R = 0.7734).

Conclusion: Our results show that the Caucasian scale is suitable for capturing photo-ageing on Chinese skin, especially wrinkle variations. The Korean dyspigmentation scale supplements the Caucasian scale to capture dyspigmentation patterns on Chinese skin that may be absent on Caucasian skin. Currently, photo-ageing scales for Chinese skin are absent. When developed, these photo-ageing scales must be properly validated for their ability to capture photo-ageing of the entire face.