Noxious heat evokes stronger sharp and annoying sensations in women than men in hairy skin but not in glabrous skin.

Abstract

Brief noxious heat evokes more intense pain in women than in men; however, sex differences in the intensity of pain sensations evoked in hairy and glabrous skins are not clearly understood. Glabrous skin putatively lacks the type of A-delta nociceptors that underlie heat-evoked sharp sensation. Therefore, we assessed whether noxious heat-evoked pain qualities differed for hairy and glabrous skins and whether sex differences exist in these evoked pains. We applied a prolonged (30s) ramped noxious heat stimulus to the dorsal and ventral aspects of the feet of 16 males and 16 females. Stimuli were calibrated in each subject to evoke a peak pain magnitude of 50/100. Subjects provided continuous online ratings of pain, annoyance, burning, sharp, stinging and cutting sensations in separate runs. The results indicate that both sex and skin type impact noxious heat-evoked sensations. Specifically, ratings of sharp sensations and annoyance evoked in hairy skin were significantly more intense in women than in men. Sharp, stinging and cutting sensations were evoked in glabrous skin, but the magnitude of these sensations was greater in hairy skin than glabrous skin; an effect only in females. Also, there was no sex difference in sharp sensation and annoyance in glabrous skin. These findings suggest that sharp sensations are evoked more prominently in hairy than in glabrous skin of women and that sharp sensations and annoyance play a prominent role in mediating aspects of pain-evoked from hairy skin in women.