REGIONAL AND INDIVIDUAL-DIFFERENCES IN CUTANEOUS SENSITIVITY TO CHEMICAL IRRITANTS - CAPSAICIN AND MENTHOL

Regional and individual differences in sensory irritation produced by capsaicin and l-menthol were assessed in two experiments. Thresholds f or irritation were measured on the forearm and cheek using a psychophy sical method that combines a bilateral, forced-choice detection task w ith an intensity scaling task. Experiment 1 showed that thresholds on the cheek were higher than on the forearm for both chemicals; on avera ge, thresholds were much lower for capsaicin than for menthol; there w ere large individual differences in thresholds for both chemicals on b oth sites; and capsaicin and menthol produced different qualities of s ensation. In contrast to earlier findings, capsaicin failed to produce itching on either site. Experiment 2 showed that itching could be evo ked on the forearm, but not the face, when capsaicin was applied in a single dose rather than in an ascending concentrations series, as it h ad been in experiment 1. It was hypothesized that the absence of itchi ng in experiment 1 was due to a more rapid desensitization for itching compared to burning and stinging, and that the lack of itching on the cheek may reflect different chemosensory innervation on facial and fo rearm skin. Overall, the results demonstrate that psychophysical measu rements can provide information about regional and individual differen ces in the susceptibility to sensory irritation from contact with envi ronmental chemicals.