The effect of ultraviolet-B exposure scheduling on the photodamage of hairless mouse skin.

In a mouse model, we investigated whether different exposure protocol of ultraviolet-B with the same total doses could induce a different degree of photodamage in mouse skin. Two different exposure frequencies, three times or six times a week, were applied under the condition of weekly same cumulative irradiation dose equally for 10 weeks. Then the photodamage parameters such as skin wrinkling, histochemical dermal change and epidermal and dermal thickness were evaluated. Wrinkle grade, histological assessment by score, and dermal thickness did not reveal any difference between the two groups. However, at irradiation week 10 epidermal thickness of the three times a week irradiation group was significantly thicker than that of the six times a week irradiation group. The same cumulative dose resulted in different epidermal thickness. Our results suggested that exposure frequency or scheduling could influence the epidermal damage by ultraviolet radiation even though the cumulative dose is equal.