Parts Used & Where Grown
Oak trees grow throughout North America. Some species of oak grow around the world, including in China and the Middle East. The bark of the oak tree is used medicinally.
How It Works
Tannins are the primary constituents of oak bark.1 These tannins are potent astringents, akin to those found in witch hazel (Hamamelis virginiana). Tannins bind liquids, absorb toxins, and soothe inflamed tissues. The oak tannin, known as ellagitannin, inhibits intestinal secretion,2 which helps resolve diarrhea. The nonirritating, astringent nature of oak has led to its recommendation for treating mild, acute diarrhea in children (along with plenty of electrolyte-containing fluids) in Europe.3 Astringents such as oak may also help relieve the pain of sore throats and canker sores.