Oak bark is widely used as an effective astringent. Oak bark is rich in galic and ellgalic acids, quertecin, flobaphen, pictines and tannins. Tannins are thought to have an astringent action, meaning that they reduce tissue swelling and stop bleeding, and they are traditionally thought to be useful for diarrhea. It has antiphlogistic, haemostatic, and antiseptic properties. Oak bark is often used topically for various skin disorders.