Abstract: Objective To study the protective effects of different sunscreen standards on skin photodamage induced by ultraviolet radiation in rats, and to provide background data for the evaluation of sunscreen efficacy of sunscreen cosmetics. Methods The skin phototoxicity damage rat models were established by ultraviolet radiation of Ultraviolet A (UVA ,4.5 mJ·cm^-2·s^-1) + Ultraviolet B (UVB,0.036 mJ·cm^-2·s^-1). The rats were irradiated twice a week for 4 weeks, and the cumulative radiation time was 440 minutes. The sunscreen standard products (S1、S2、P2、P3 and P7)were applied 30 minutes before each exposure. After the experiment, the skin was observed histopathologically and the expression of Melanoma marker (human), mAb (HMB45) was detected by immunohistochemistry. Results Compared with the model group, the four indexes of epidermal thickening, sebaceous gland hyperplasia, skin injury score and HMB45 expression in group S2 were significantly alleviated; the three indexes of epidermal thickening, skin injury score and HMB45 expression in group P3 and group P2 were significantly alleviated compared with the model group; the two indexes of skin thickening and skin injury score in group S1 were significantly alleviated compared with the model group. In the group P7, only one index of epidermal thickening was significantly reduced compared with the model group. Generally speaking, the protective effect of the standard conforms to the values of PFA and SPF. Conclusions The protective effect of sunscreen cosmetics on skin photodamage caused by ultraviolet radiation is related to PFA and SPF values. This method can be used to evaluate the sunscreen efficacy of sunscreen cosmetics.

Key words: Ultraviolet A (UVA), Ultraviolet B (UVB), Skin phototoxicity, Sunscreen standard