Red onions are packed with quercetin:
Red and yellow onions are one of the best natural sources of quercetin, a bioflavonoid that is particularly well suited for scavenging free radicals. Aside from its antioxidant properties, quercetin has been found to possess cancer fighting, anti-fungal, anti-bacterial, and anti-inflammatory properties. It has shown promising potential for preventing and controlling the formation of intestinal polyps, suppressing the rhinoviruses that are the underlying cause of common cold, treating psoriasis, and inhibiting the replication of viruses including the herpes simplex virus that can cause cold sores. It has also been shown to reduce the risk of stomach cancer: according to one study, half an onion a day could reduce the risk of stomach cancer by 50%.
Allicin in onions fights regenerative diseases and fungi:
In addition to quercetin, red onions provide allicin, a potent health-promoting compound that is found in onions and other members of the Allium family when the plant is crushed or chopped. Allicin has been shown to promote cardiovascular health, prevent and treat cancer, and reduce high blood pressure. It has also been suggested that allicin could be helpful for people with dandruff due to its anti-fungal properties.