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, anti-inflammatory agent, and skin-healing ingredient, likely owing to the stimulating effect it has on the immune system, of which skin is our body’s first line of defense. 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.
More good news on the skincare front: Quercetin can help defend skin from UVB-related damage, reduce the production of an elastin-degrading enzyme, and help heal and improve the appearance of scars. [3,4,5]
- 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.
- Lin C, Leu Y, Al-Suwayeh S, Ku M, Hwang T, Fang J. Anti-inflammatory activity and percutaneous absorption of quercetin and its polymethoxylated compound and glycosides: the relationships to chemical structures. Eur J Pharm Sci. 2012;47(5):857-64.
- Cho J, Cho S, Lee S, Lee K. Onion extract and quercetin induce matrix metalloproteinase-1 in vitro and in vivo. Int J Mol Med. 2010;25(3):347-52.
- Phan T, Lim I, Chan S, Tan E, Lee S, Longaker M. Suppression of transforming growth factor beta/smad signaling in keloid-derived fibroblasts by quercetin: implications for the treatment of excessive scars.. J Trauma. 2004;57(5):1032-7.
Ginkgo biloba leaf extract
St. John's wort