Abstract: 【Abstract】 Objective To determine the action spectrum of ultraviolet in chronic actinic dermatitis (CAD) and further analyze the influence of course of disease and period in the sunlight everyday on the decrease of minimal erythema dose (MED) respectively. Methods The MEDs of Ultraviolet A (UVA) and Ultraviolet B (UVB) were measured by SUV 1000 type ultraviolet simulator in 108 presumptive cases of CAD. Results 97 of 108 cases were diagnosed as CAD by a lower UVA-MED and/or UVB-MED. A lower UVA-MED was found in 85.57% of the 97 cases, ranging from 1.02～23.97J/cm2, while a lower UVB-MED in 70.10%, ranging from 1.94～19.23 mJ/cm2. Out of 97 cases, 29.90% was found to be sensitive to UVA alone and 14.43% to UVB alone. As for the course of disease of 97 cases, the MED of action spectrum in above-5-year group was significantly lower than that in 3～5-year group or in <3-year group (P<0.01), while there was no difference of MEDs of action spectrum between 3～5-year group and <3-year group. And for period in the sunlight, the MED of action spectrum in >7-hour/day group was significantly lower than that in 5～7-hour/day and in <5-hour/day group (P<0.01), while no difference of MEDs of action spectrum was found between 5～7-hour/day group and <5-hour/day group (P>0.05). Conclusions UVA alone, as the action spectrum in CAD, should never be ignored. Moreover, the development of course of disease and prolongation of period in the sunlight will further result in the decrease of MED of action spectrum.

Key words: Chronic actinic dermatitis, Ultraviolet, Minimal erythema dose