Cutaneous reactions to substance P and histamine in atopic dermatitis.

The flare and weal reactions to intradermal injections of histamine and the peptide substance P were measured in a group of patients with atopic dermatitis and compared to reactions in a non-atopic control group. There was no significant difference in the flare areas between the controls and atopics with either reagent. The weal volumes after injection of substance P and histamine were significantly larger in the atopic group. As substance P causes mast cell histamine release, the increased weal volumes produced by substance P in the atopics may be entirely due to the exaggerated atopic weal reaction to histamine.