The immediate and long-term effects of applying capsaicin to cutaneous nerves.

Capsaicin has now been shown to have a neurotoxic action on C-fibres in adult rodents and several other mammalian species. In the adult the effect is preferentially on nociceptive C-fibres. The hypoalgesia and loss of neurogenic inflammation that follow capsaicin treatment are likely to be a direct consequence of the C-fibre loss. In addition to its long-term toxic action, capsaicin also has an immediate effect on conduction in nociceptive C-fibres. This action probably produces the short-term hypoalgesia and loss of antidromic plasma extravasation that follow application of capsaicin to peripheral nerves.