Bioflavonoid ingredient from plants. Quercetin occurs naturally in red wine, tea, onions, kale, tomatoes, berries, and many other fruits and vegetables, with the highest concentrations found in the leaves and skins. It functions as an antioxidant, skin-soothing agent, and restorative ingredient. Quercetin is present in some herbal ingredients, too, including St. JohnŠ—Ès wort and Ginkgo biloba.
In terms of skincare, research has shown that a lipid-based delivery system is optimal for quercetin to exert antioxidant benefits. Even more exciting, this type of formula provides an initial burst of quercetin followed by sustained release over a 24-hour period. When quercetin is mixed with silicone and lipids, the intake is greater, as confirmed by testing on human skin.
References for this information:
International Journal of Pharmacology, January 2013, issues 1-2, pages 56-66
Skin Pharmacology and Physiology, 2013, issue 2, pages 57-67