Soy Isoflavones

Soy isoflavones are antioxidant/phytoestrogenic actives typically used at low percentages in leave-on products, where they are generally well-tolerated but not completely inert. In patch testing and real-world use, soy-derived actives can trigger irritation or allergic contact dermatitis in a minority of sensitive or atopic individuals due to residual soy proteins/extract complexity and individual allergy history. Given the potential for delayed sensitization in highly reactive eczema-prone patients, I rate them as mild rather than gentle. Safety Notes: In commercial skincare, soy isoflavones are most often delivered via soybean extract blends, with finished-product isoflavone levels commonly landing around 0.01–0.2% in mass-market moisturizers/eye creams and anti-aging serums (low end driven by cost, color/odor constraints, and use as a supporting antioxidant/brightening active). Higher-strength consumer-available “isoflavone” or “genistein/daidzein” targeted treatments can reach about 0.5–2.0% total soy isoflavones in leave-on products, generally using standardized extracts or purified fractions to maintain stability and aesthetics. Rinse-off products typically sit at the lower end because of short contact time and reduced incentive to load actives.