Astringent is a substance that helps to stop the outflow of internal body fluids, especially of blood or mucus.
Astringents may work in a number of ways:
  1. By making the blood vessels smaller;
  2. By helping the blood to coagulate; or
  3. By removing the water that is essential to the formation of mucus.
They are important in treating bleeding from the nose and throat, bleeding from surface wounds, and surface ulcers.
The most common astringents are metallic astringents (for example, copper sulfate, silver nitrate, or calcium carbonate); epinephrine, natural and synthetic; vegetable astringents (such as witch hazel); and substances containing alcohol (for example, cologne).