Capsaicin

Capsaicin is a potent TRPV1 agonist used topically for analgesia (often ~0.025–0.1% in creams and up to 8% in patches) and is intrinsically noxious to skin, commonly causing intense burning, stinging, erythema, and neurogenic inflammation even at low concentrations. Clinical experience and labeling for capsaicin products consistently reflect frequent, expected irritation and discomfort, which is amplified in eczema, barrier-compromised, or post-procedure skin. Given the predictable high irritation burden and risk of severe flare in sensitive populations, it warrants the maximum irritancy score. Safety Notes: In consumer skincare, capsaicin is typically used at extremely low levels in “warming/tingling” leave-on creams, massage gels, and lip-plumping style products, with the lowest marketed formulas often around ~0.5 ppm (0.00005%) to deliver a perceptible sensory effect while limiting irritation. High-strength OTC topical analgesic/rubefacient creams and patches available to the general public commonly use about 0.025–0.1% capsaicin, with ~0.1% representing the upper end seen in non-prescription products; higher percentages (e.g., 8%) are generally restricted to prescription/professional use and are excluded. Rinse-off cosmetics rarely use meaningful capsaicin levels due to irritation risk and limited benefit, so the observed market range is driven primarily by leave-on products.