Potent antioxidant and anti-inflammatory agent for skin.  Soy is one of many phytochemicals (phyto = plant) chemicals that are biologically active against free radicals. Soy extract’s increasing use in anti-aging products is largely due to studies showing that its antioxidant genistein (a component of soy) has a collagen-stimulating effect and that various compounds in soy influence skin thickness and elasticity. [2,3]
Researchers have also looked at Bifidobacterium-fermented soy milk extracts. On mouse skin and in human skin fibroblasts (lab cultured), this bacteria-modified form of soy was shown to stimulate the production of hyaluronic acid in skin. This was due to the amount of genistein released during the fermentation process. [3,4]
Soy extract has been shown to help reduce the effects of UVB exposure on human skin cells. [5,6]
Research hasn’t shown that soy extract or soy oil has estrogenic effects when applied to skin, as it can when taken orally. 
- Stallings ALM. Practical Uses of Botanicals in Skin Care. J Clin Aesthet Dermatol. 2009;2(1):36-40.
- Schmid D, Zülli F. Topically-Applied Soy Isoflavones Increase Skin Thickness.. Cosm & Toil. 2002 45-50.
- Miyazaki K, Hanamizu T, Sone T, Chiba K, Kinoshita T, Yoshikawa S. Topical application of Bifidobacterium-fermented soy milk extract containing genistein and daidzein improves rheological and physiological properties of skin. J Cosmet Sci. 2004;55(5):473-9.
- Südel K, Venzke K, Mielke H, Breitenbach U, C M, Jaspers S, Koop U, Sauermann K, Knussman-Hartig E, Moll I, et al. Novel aspects of intrinsic and extrinsic aging of human skin: beneficial effects of soy extract. Photochem Photobiol. 2005;81(3):581-7.
- Park N, Park J, Kang Y, Bae J, Lee H, Yeom M, Cho J, Na Y. Soybean extract showed modulation of retinoic acid-related gene expression of skin and photo-protective effects in keratinocytes. Int J Cosmet Sci. 2013;35(2.):136-42.
- Chiang H, Wu W, Fang H, Chen B, Kao T, Chen Y, Hung C. UVB-Protective Effects of Isoflavone Extracts from Soybean Cake in Human Keratinocytes. Int J Mol Sci. 2007;8(7):651-661.
- Toxicology. IJo. Final report of the amended safety assessment of PEG-5; -10; -16; -25; -30; and -40 soy sterol. Int J Toxicol. 2004;23(S2):23-47.