Systemic effect of ultraviolet irradiation on non-immunologic immediate contact reactions to benzoic acid and methyl nicotinate.

Systemic effects of ultraviolet irradiation B (UVB) and ultraviolet irradiation A (UVA) on non-immunologic immediate contact reactions (NIICRs) induced by benzoic acid (BA) and methyl nicotinate (MN) were studied in healthy volunteers. NIICR tests with four concentrations of BA and MN in white petrolatum were performed on the skin of the upper back on exposed and non-exposed areas, before and at intervals 1-14 days after exposure to 1) 0.20 J/cm2 of UVB, 2) after the first of daily doses on five consecutive days of 0.04 J/cm2 of UVB, 3) after the first of daily doses on five consecutive days of 20 J/cm2 of UVA, and 4) 1-8 weeks after the first of twelve consecutive doses of 20 J/cm2 of UVA given three times a week over a period of four weeks. After the last of twelve exposures of UVA, stratum corneum was stripped off from both the exposed and the non-exposed skin. Forty minutes after application of the test substances, erythema and edema reactions were observed visually, and changes in the blood flow were monitored using a laser-Doppler flow-meter. All dosages of UV-light inhibited the NIICRs on exposed areas. UVB as given repeatedly inhibited NIICRs to 125 mM BA on non-exposed areas. The twelve doses of UVA also had a systemic inhibitory effect on NIICRs both on stripped and non-stripped test areas. The results indicate a systemic inhibitory effect of UV light on NIICRs.