Influence of UVA pre-exposure on UVB-induced erythema - A chromometric study

We examined the influence of ultraviolet A (UVA) pre-exposure on UVB minima l erythemal dose in 9 Caucasian subjects. Three zones were tested. One zone received only UVB, the second zone received a low UVA dose + UVB, and the third zone received a high UVA doset + UVB. Each zone was divided into 9 ci rcles receiving increasing doses of UVB in order to obtain 3 different UVA- exposed series of 9 circles. Visual and chromometric readings were performe d 24 h later. Pre-exposure to UVA caused variations in the slope of the dos e-response curve (colorimetric index as a function of the UVB dose). In rel ation to UVB erythema, these variations indicated a protective effect for 6 /9 subjects and an aggressive effect for 3/9 subjects, No predictive criter ia were found for inclusion within a group.