Flavonoids (or bioflavonoids) (from the Latin word flavus meaning yellow), also collectively known as Vitamin P and citrin, are a class of plant secondary metabolites or yellow pigments having a structure similar to that of flavones. Flavonoids are widely distributed in plants fulfilling many functions.
The widespread distribution of flavonoids, their variety and their relatively low toxicity compared to other active plant compounds (for instance alkaloids) mean that many animals, including humans, ingest significant quantities in their diet. Preliminary research indicates that flavonoids may modify allergens, viruses, and carcinogens, and so may be biological "response modifiers". In vitro studies show that flavonoids also have anti-allergic, anti-inflammatory, anti-microbial, anti-cancer, and anti-diarrheal activities.