Soy isoflavones are plant compounds, most notably genistein and daidzein, that are shaped similarly enough to the hormone estrogen that they can weakly latch onto estrogen receptors in skin, especially the type found on the cells that build collagen and form the outer skin layer.
Animal studies modeling declining estrogen levels, similar to what happens around menopause, have found that isoflavone treatment boosts collagen production and increases the skin's natural hyaluronic acid levels, helping offset the thinning and dryness that comes with falling estrogen.
Genistein on its own has also shown antioxidant activity and can help limit UV triggered activation of the enzymes that break down collagen. Most of the strongest evidence for these effects comes from oral isoflavone supplements or from animal studies with surgically induced estrogen decline, rather than from topical use in people, so while the underlying biology is well supported, direct human evidence for topical skincare use is thinner.
Soy Isoflavones References
Genistein aglycone, a soy derived isoflavone, improves skin changes induced by ovariectomy in rats, British Journal of Pharmacology, 2012
Effects of Isoflavones on the Skin of Postmenopausal Women, A Pilot Study
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