Effect of skin pigmentation on the response to intradermal histamine

The effects of injecting histamine phosphate, in serial 10-fold dilutions ranging from 0.0001 to 0.1 mg/ml histamine base, intradermally into three groups of nonatopic healthy volunteers with varying degrees of skin pigmentation were studied. The wheal sizes in the 30 Negroid subjects with darkly pigmented skins were consistently greater than those in both the 30 Caucasian subjects with light skin pigmentation and the 15 mixed Caucasian/Negroid subjects with light brown skins. The overall wheal response was the smallest in the Caucasian subjects. The differences in wheal sizes were greatest between the Negroid and Caucasian subjects for all dilutions, and these differences were statistically significant (p < 0.005). From this study it appears that skin pigmentation has a profound effect on the wheal response to intradermally injected histamine. It is speculated that this difference in response may be related to the melanin pigment in the skin.