Ultraviolet light inhibits nonimmunologic immediate contact reactions to benzoic acid

The effect of ultraviolet B (UVB) and ultraviolet A (UVA) irradiation on nonimmunologic immediate contact reactions (NIICRs) induced by benzoid acid (BA) was studied in 14 and 13 test subjects, respectively. 10 x 20 cm areas of the back skin were irradiated with 0.08, 0.16, and 0.24 J/cm2 UVB, and with 20 and 60 J/cm2 UVA. Five concentrations of BA were applied to the UV-exposed and nonexposed areas on the 1st, 3rd, 7th, and 21st day after UVB irradiation and on the 1st, 3rd, 7th, and 14th day after UVA irradiation. Forty minutes after BA application, erythema and edema reactions were observed visually, and changes in the skin blood flow were monitored using laser-Doppler flowmetry. The highest dose of UVB significantly inhibited NIICRs for 3 weeks. The lower doses of UVB had a weaker effect. Both doses of UVA diminished blood flow in NIICRs to lower concentrations of BA for 14 days.