Abstract: Objective: To determine the minimum erythema dose (MED) on rabbit ear irradiated by 308 nm excimer laser. Methods: The left ears of 30 rabbits were irradiated with the 308 nm eximer laser and the right ears were taken as the negative controls. The irradiation doses of the eximer laser on the left ears were 150, 300, 450, 600, 900 and 1350 mJ/cm2. Then the average MED after 24 h, 48 h and 72 h in 30 rabbitswas calculated, and the micro-structure was observed under transmission electron microscopy (TEM), at 96 h after irradiation. Results: The average MED after 24 h, 48 h and 72 h was 300±55.39 mJ/cm2. Compared with non-irradiated areas, the MED area after 96 h irradiation showed that the epidermis and dermis were thick,edema,and angiotelectasis.The blood vessels were infiltrated with lots of inflammatory cells. Under TEM, in the MED area irradiated after 96 h, there were degeneration and disorganization of collagen fibres, and fibrocyte organelle was coalesced presenting as crumby degeneration. Around blood vessels there was infiltration with inflammatory cells and erythrocyte exosmosis. Erythema gradually regressed in 96 h and disappeared in 10-14 days, without any large area of necrosis in pathology and TEM. Conclusion: 308 nm eximer laser is highly stability and safety.

Key words: 308 nm excimer laser, MED, sunscreen