Potent antioxidant and anti-inflammatory agent for skin (Sources: Cancer Investigation, 1996, volume 14, number 6, pages 597–608; Skin Pharmacology and Applied Skin Physiology, May–June 2002, pages 175–183; and Journal of the American Academy of Dermatology, June 2005, pages 1049–1059).
Soy is one of many phyto (i.e., plant) chemicals that are biologically active against free radicals. Polyphenol compounds, such as the catechins found in green tea, also fit this profile.
Soy extract’s increased use in anti-aging products is largely due to studies showing that genistein (a component of soy) has a collagen-stimulating effect and that various compounds in soy influence skin thickness and elasticity (Sources: Cosmetics & Toiletries, June 2002, pages 45–50; and Journal of Cosmetic Science, September–October 2004, pages 473–479). 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 production of hyaluronic acid in skin. This was due to the amount of genistein released during the fermentation process (Sources: Skin Pharmacology and Physiology, 2003, pages 108–116; and Photochemistry and Photobiology, May-June 2005, pages 581–587).
Studies performed on mouse skin have shown that topical application of soy milk and other soy compounds has a protective effect against UVB light damage. It is theorized that these benefits will translate to human skin as well, but conclusive evidence has not yet materialized (Sources: Oncology Research, volume 14, numbers 7/8, 2004, pages 387–397; and Photodermatology, Photoimmunology, & Photomedicine, April 2003, page 56).
There is no research showing that soy extract or soy oil has estrogenic effects when applied to skin, as it can when taken orally (Source: International Journal of Toxicology, 2004, volume 23, Supplement 2, pages 23–47). Some companies have asserted that soy can affect hair growth and lighten skin color when applied topically. The single study citing this was done by Johnson & Johnson, the company that sells products claiming to have this effect (Source: Experimental Dermatology, December 2001, pages 405–413).