Equol

Equol is a soy-derived isoflavone metabolite used as an antioxidant/estrogen-receptor modulator in topical anti-aging products, typically at low concentrations (about 0.1–1%). Available human-use data and typical cosmetic safety experience suggest low rates of stinging or erythema at these levels, with irritation more likely from the formula vehicle than equol itself. Because it is a bioactive polyphenol and soy-derived (rare allergy/sensitization is possible in highly reactive patients), I rate it very gentle rather than exceptionally gentle. Safety Notes: In consumer skincare, equol is typically used as a low-dose antioxidant/anti-aging active in leave-on serums and creams, with effective/marketed levels often in the ~0.01–0.2% range; some formulas list it near the end of the INCI, consistent with ~0.001–0.01%. High-strength OTC products positioned as hormone-related/menopause or advanced anti-aging treatments are observed up to about 0.5–1% equol in leave-on systems, with higher levels uncommon due to cost, sourcing, odor/color, and stability considerations; rinse-off use is rare and generally at the low end.