Substance P provokes cutaneous erythema and edema through a histamine-independent pathway.

Substance P is a neuropeptide (contained in/and released from the A delta and C nerve fibers of the skin), which provokes erythema, edema, and pruritus after intradermal injection. Local pretreatment with capsaicin produces decreased substance P-dependent erythema, with edema similar to that observed before pretreatment with capsaicin. We injected histamine and in a parallel experiment, substance P in five volunteers before and after local treatment with capsaicin, with 48/80, after 5 days of hydroxyzine. The injection of SP provoked erythema centered by a wheal. After treatment with 48/80, SP provoked increased erythema and a wheal. After hydroxyzine treatment, the injection of histamine produced no erythema or edema in four of the five subjects, while SP provoked erythema in all five subjects and edema similar to that observed before treatment with hydroxyzine. These data support the hypothesis that substance P provokes erythema and edema both with histamine-dependent and histamine-independent pathways.