Vascular and sensory responses of human skin to mild injury after topical treatment with capsaicin.

1 Immediately after several topical applications of capsaicin at 2-hourly intervals, human forearm skin would no longer develop flare (vasodilation) around a small injury. At the same time heat pain thresholds were reduced on average by 3.5 degrees C. These results are consistent with block by capsaicin of the effector side of the axon reflex, perhaps by depleting nerve terminals of substance P. 2 Over a period from several days to several weeks after treatment, flare was diminished and heat pain thresholds were slightly elevated. These changes may be due to long-lasting damage of cutaneous nerve terminals by capsaicin.