Abstract: Objective To observe the alteration of skin complexion after UVA and UVB exposure. Methods The back skin of ten females with skin type Ⅲ was subjected to single exposure to solar-simulated UVA of double minimal persistent pigment darkening （MPPD） or UVB of double minimal erythema dose （MED）. Skin reflectance was assessed with clinical grading, spectcolometer and Mexameter MX 18 before irradiation, 6 hours, 1, 7 and 14 days after the irradiation. Results After UVB irradiation, a* value and erythema index （EI） abruptly increased at 6 hours and peaked on day 2; L* value sharply declined on day 1; ITA° markedly decreased on day 7; melanin index （MI） declined within the first 2 days, but notably increased on day 7. After UVA irradiation, a* and EI value experienced no apparent changes; L* value obviously declined at 6 hours; ITA° reached its lowest value on day 14; MI increased only on day 1. Conclusions There is a significant difference in the kinetics and extent of skin complexion changes after UVA and UVB irradiation. EI and a* value are sensitive and accurate indices for evaluating sunburn, and MI and ITA° for analyzing tanning.

Key words: Ultraviolet