Influence of ultraviolet light on itch and flare reactions in human skin induced by histamine and the histamine liberator compound 48/80.

The itch and flare responses induced by intradermal injection of histamine and the histamine liberator compound 48/80 were studied in healthy volunteers before and after exposure to UVB, UVA or PUVA administered 2-3 times weekly for 4 weeks. All three modalities were found to inhibit the responses induced by compound 48/80. The degree of tanning was most pronounced after PUVA and weakest after UVB, without any correlation between tanning and inhibition of itch. In contrast, when induced by histamine, the responses were not inhibited to the same extent, pronounced and significant inhibition being observed only for itching in subjects exposed to UVB. It is concluded that UVB, UVA and PUVA all might be of benefit in treating pruritic states if histamine release is involved and that UVB might have an additional effect by inducing hyposensitivity to itching stimuli.