Ultraviolet-induced suppression of the primary allergic reaction. Four times the minimal erythema dose of ultraviolet B administered 24 hours prior to sensitization.

The effect of localized irradiation with 4 times the minimal erythema dose (MED) of ultraviolet B (UVB) 24 h prior to sensitization with dinitrochlorobenzene (DNCB) was examined. In a placebo-controlled design, 9 of 19 subjects were locally irradiated on the right buttock; 24 h later, DNCB (1000 micrograms) was applied to the right buttock in all 19 subjects, and subjects were examined 7 and 14 days later for the development of a primary allergic response (PAR). In those not developing a PAR, a challenge dose of DNCB (50 micrograms) was applied to the volar forearm and examined 2 days later for an elicitation response. A statistically significant difference was seen in the number of subjects developing a PAR, comparing the group irradiated with UVB versus the group not irradiated (33% vs 80%). There was no statistically significant difference seen in elicitation responses between the 2 groups. We have shown that intense localized UVB irradiation as early as 24 h prior to sensitization with a potent allergen at this site may inhibit the PAR but does not appear to affect the elicitation response at a distant site.