Red and yellow onions are one of the best natural sourcesof quercetin, a bioflavonoid that is particularly suited to scavenge freeradicals. Apart from its antioxidant properties, quercetin has been found tohave anti-cancer, anti-fungal, anti-bacterial, and anti-inflammatoryproperties. It is shown promising potential to prevent and control theformation of intestinal polyps, removing rhinoviruses are the underlying causeof cold treatment of common psoriasis, and inhibition of virus replication,including virus herpes simplex which can cause cold sores. It has also beenshown to reduce the risk of stomach cancer: According to one study, half of anonion one day could reduce the risk of stomach cancer by 50%.