Quantitative Assessment of Ultraviolet-Induced Erythema and Tanning Responses in the Han Chinese Population

Ultraviolet radiation (UVR) can induce erythema and tanning responses with strong diversity within and between populations, but there were no precise method for evaluating the variation in these responses. In this study, we assessed the time course of ultraviolet (UV)-induced responses based on the erythema index (EI) and melanin index (MI) over 14 consecutive days in a pilot cohort study (N = 31). From safety evaluations, we found that no skin blisters occurred at a UV dosage of 45 mJ/cm 2 , but there were significant skin reactions. Regardless of UV dosage, the measurements and variances of EI peaked on day 1 after UV irradiation, and those of MI peaked on day 7. Dose–response curves, including erythema dose–response (EDR) and melanin dose–response (MDR), could measure UV-induced phenotypes sensitively but more laboriously. As an alternative, we directly represented the UV-induced erythema and tanning responses using the erythema increment (ΔE) and melanin increment (ΔM). We found that ΔE and ΔM at 45 mJ/cm 2 significantly correlated with erythema dose–response (EDR) ( R 2 > 0.9) and melanin dose–response (MDR) ( R 2 > 0.9), respectively. Therefore, ΔE and ΔM on day 1 and day 7 after UV irradiation at a dosage of 45 mJ/cm 2 might be ideal alternative measures for assessing individual erythema and tanning responses. Then, a second cohort (N = 664) was recruited to validate the UV-induced phenotypes, and, as expected, the results of the two cohorts were in agreement. Therefore, we developed a simplified and precise method to quantify the UV-induced erythema response and tanning ability for the Han Chinese population.