Ethnic differences in pain, itch and thermal detection in response to topical capsaicin: African Americans display a notably limited hyperalgesia and neurogenic inflammation

Abstract

Topical application of capsaicin commonly produces burning, stinging and itching as well as hyperalgesia to heat stimuli via activation of transient receptor potential vanilloid subtype 1. To investigate whether there are differences in sensory response and neurogenic inflammation to topical capsaicin in four different ethnic populations with different skin types. The study was performed in 40 healthy subjects consisting of 10 African Americans, 10 East Asians, 10 Hispanics and 10 Caucasians. Warmth sensation and heat pain detection thresholds, as well as pain intensity, were measured before and after application of capsaicin or placebo on forearms along with skin blood flow and the extent of the flare reaction. In African Americans the heat pain detection threshold, pain intensity and skin blood flow did not change significantly after capsaicin application, while in the other three ethnic groups a significant change occurred characterized by hyperalgesia and vasodilatation. The postcapsaicin warmth sensation threshold increased in African Americans and decreased in Hispanics, the latter also uniquely experiencing postcapsaicin itch. Our observations indicate that African Americans display a limited hypersensitivity following topical capsaicin, compared with the three other ethnic groups.