If you're using capsaicin, it may be time to reconsider; discuss this with your doctor.

Topical application of capsaicin - the active component in chili peppers - causes cutaneous autonomic nerve fibers to degenerate, according to a November 8th online paper in the Annals of Neurology.

In light of these findings, Dr. Roy Freeman told Reuters Health by email, capsaicin should be used cautiously on skin that's at risk for ulceration, "particularly in neuropathic conditions characterized by sensory and autonomic impairment."

Dr. Freeman and colleagues at Beth Israel Deaconess Medical Center, Boston, followed 20 healthy young adults who had 0.1% capsaicin cream applied under an occlusive dressing for 48 hours. Another 12 subjects had placebo cream applied.

A series of skin biopsies over the next six months showed that the treatment group had significant reductions in sudomotor, vasomotor, pilomotor, and sensory function compared to the placebo group. The treatment group also had significant reductions in the fiber densities in the corresponding nerves.

Sensory function and intra-epidermal nerve fiber density reached their nadirs by day 6. Autonomic function and autonomic nerve fiber density had declined maximally by day 16.

The autonomic nerves generally regenerated within 40 to 50 days, whereas sensory fibers required 140 to 150 days to return to baseline. This finding suggests the factors underlying capsaicin-induced damage may differ in autonomic and sensory nerve fibers, the authors note.

They also point out that the study protocol "does not represent the typical clinical use of capsaicin when prescribed for neuropathic pain." Typical use might, for example, consist of 0.025% or 0.075% applied several times a day for several weeks. (On the other hand, the FDA recently approved a new high-dose transdermal patch for patients with postherpetic neuralgia; Qutenza (NeurogesX, Inc.), containing 8% capsaicin, is applied for one hour and reportedly provides up to three months of pain relief.)

Future research, which more closely reflects the clinical use of capsaicin, "should be performed to examine the effects of capsaicin on intra-epidermal and subepidermal nerve structure and function," the authors conclude.

Ann Neurol. Posted online November 8, 2010. Abstract

David Douglas • Reuters Health Information © 2010