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. John’s 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.
- Bose S, Du Y, Takhistov P, Michniak-Kohn B. Formulation optimization and topical delivery of quercetin from solid lipid based nanosystems. Int J Pharm. 2013;441(1-2):56-66.
- Scalia S, Franceschinis E, Bertelli D, Iannuccelli V. Comparative Evaluation of the Effect of Permeation Enhancers, Lipid Nanoparticles and Colloidal Silica on in vivo Human Skin Penetration of Quercetin. Skin Pharmacol Physiol. 2013;26(2):57-67.
Ginkgo biloba leaf extract
St. John's wort