Quercetin is a naturally occuring flavonoid. Quercetin has antioxidant, antiviral and anti-allergy effects. The antioxidant effect is attributed to the cathechol-B-ring and the location of the hydroxyl substitutions. Quercetin has demonstrated activity against some viruses. This is attributed to quercetin’s ability to reduce the infectivity of viruses and blocking viral replication. Quercetin has also been shown to have a positive effect on the human immune system. Possibly by increasing neutrophil chemotaxis, macrophage phagocytosis, natural killer cell lytic activity, and mitogen-stimulated lymphocyte proliferation. Quercetin has also been shown to have anti-allergy effects attributed to the fact that it may affect mast cell proliferation and secretory granule development.