Tannic acid is a polyphenolic compound. It is a type of the commercially available tannins. It acts as a weak acid. Tannic acid is found in the nutgalls formed by insects on twigs of certain oak trees (Quercus infectoria and other Quercus species). It is removed and used as medicine. In the old days it was used as antidote against different poisons. Nowadays, tannic acid is applied topically for the treatment of cold sores, diaper rash, fever blisters and poison ivy. Tannic acid is also taken by mouth and applied directly for bleeding, chronic diarrhea, dysentery, bloody urine, painful joints, persistent coughs, and cancer.