Assessment of pepper spray product potency in Asian and Caucasian forearm skin using transepidermal water loss, skin temperature and reflectance colorimetry.

Historically, pepper spray product potency has been established using a taste test evaluation. A taste test is subjective and may not be appropriate for assessing pepper potency in skin. The current study evaluated chemically diverse pepper sprays in human forearm skin using three objective, noninvasive parameters: transepidermal water loss, skin surface temperature and erythema, as a means for assessing dermal pharmacology, toxicology and product potency. Five commercial pepper spray products containing various capsaicinoid analogs at various concentrations were evaluated in duplicate on volar forearms of six Caucasians and six Asians using a 10 min exposure. Mean surface skin temperature, transepidermal water loss results were highly variable and therefore did not demonstrate dose responsive behavior to increasing capsaicinoid concentrations. Erythema, as measured by increases in a* (reflected light in the red-to-green color spectrum) of the L*a*b* uniform color scale, was superior among parameters evaluated in discriminating pepper spray potency and correlated well with the relative and total capsaicinoid concentration in the products. Products containing greater than 16 mg ml(-1) capsaicinoid concentration produced greater erythema responses in Caucasians than Asians. Asians responded greater to the synthetic analog, nonivamide, than to mixtures of capsaicinoids, while Caucasians responded equally to both capsaicinoid analogs. Thus, pepper spray product potency in human skin reflects the total capsaicinoid concentration, the specific capsaicin analog(s) present, and the race of the individual exposed. The finding that the reflectance colorimeter a* scale can differentiate these parameters in skin will have a significant impact on evaluating the use and efficacy of pepper spray products in humans.