Daidzein

Daidzein is a soy-derived isoflavone used in cosmetics primarily as an antioxidant/skin-conditioning agent, typically at low concentrations (generally well under 1%). Available safety and patch-test data for isoflavones suggest low irritancy for most users, but plant-derived phenolics can still trigger irritation or allergy in highly reactive or soy-sensitized individuals, so it is best classified as gentle rather than exceptionally gentle. Safety Notes: In commercial skincare, daidzein (a soy isoflavone) is most often used in leave-on anti-aging/brightening products at very low levels (around 0.001–0.05%) as part of broader botanical/isoflavone complexes or when cost/solubility and odor/color constraints require minimal dosing. Dedicated “soy isoflavone/phytoestrogen” serums and some K-beauty/J-beauty actives push higher, typically ~0.1–1%, with a small number of consumer-available high-strength concentrates reaching about 2% where solubilization and stability are carefully managed. It is uncommon in rinse-off products and, when present, tends to sit at the low end due to short contact time.