Quercetin is a flavonol, a type of flavonoid with very powerful antioxidant and anti-inflammatory properties found in many fruits, as apple, green and black tea, onions, leaves, vegetables and even grains, but really known to be the flavonoid contained on apple peal.
Quercetin is also naturally available in red wine and in some fruits and vegetables present in the Mediterranean diet  It has a direct influence in the color of the herbs, fruits and plants rich in this flavonoid.
QUERCETIN FROM APPLES
Apples (mainly apple peel) are rich in quercetin, a flavonol from the group of flavonoids, which where discovered in 1938 by the Hungarian scientist Albert Szent Byorgyi. This type flavonoid is known for its anti-inflammatory and antioxidant properties, but it has also many other benefits for our bodies. It isn't strange that apples got such a good name and are known for its positive health benefits.
QUERCETIN FOR DOGS - ANTIHISTAMINIC PROPERTIES-
In spite the use of Quercetin for dogs is not very popular, Quercetin is also found in many commercial brands of dog food, used as a supplement . It has antihistaminic properties and is, together with Vitamin C, good for allergies , mainly due to the natural properties it exerts inhibiting cells from releasing histamines , a natural byproduct or biomolecule released by damaged cells as a consequence of allergic reactions. The absorption of Quercetin and isoquercitrin happens mainly in the small intestine.
In a study done in rats, the administration of 50mg per kg of weight of quercetin exerted powerful antioxidant properties, inhibiting the free radicals produced during ischemia reperfusion , a syndrome produced after organs are deprived from blood circulation during medical interventions or transplant of organs.
QUERCETIN AND ERECTILE DYSFUNCTION
Last but not least, quercetin has been studied for the positive effects that it exerted in the treatment of erectile dysfunction. The study, performed in rats, showed how the administration of regular doses of quercetin in diabetic rats ameliorated erectile dysfunction symptoms on those ones .