The clinical effect of percutaneous histamine on allergic contact dermatitis elicited to fragrance mix.

Histamine (2-(4-imidazol)ethylamine) has been shown to downregulate cell-mediated reactions in vitro. However, the rôle of such downregulation in vivo has not yet extensively been studied in humans. In an attempt to gain more insight into this, we studied in vivo the effect of percutaneous histamine on an allergic contact reaction elicited to fragrance mix in 28 human volunteers with previously-known sensitization (patch tests) to this allergen. Histamine (0.1 mg/ml) was administered either via subcutaneous injections or by scratching at the site of patch tests to one concentration (8% pet.) of fragrance mix at different times. Histamine and control solution were administered immediately before patch testing (0 hours) or 2x at 0 and 24 h (after application). No significant differences were observed in the grade of delayed-type hypersensitivity reaction (DTHR) to fragrance mix (8% pet.) by visual reading when histamine or control solution was administered. This study did not exclude the possibility that histamine could inhibit DTHR to lower concentrations of the allergen used, and therefore additional in vivo studies are required.