Tannins are in pretty much all plant. They are astringents and can be used to protect damaged tissue, dry up water, stop bleeding, or tighten overly relaxed tissue. Tannin is what causes that dry and puckered feeling you mouth after eating unripe fruit, drinking red wine or overbrewed strong black tea.
Varicose veins, Eczema, diarrhea
Apples, dark chocolate, grapefruit, pomegranates, grapes, and strong black tea, to name a few.
Interesting tidbit...You experience tannins when you drink wine. The dryer the sensation in your mouth, the higher the amount of tannin in the wine - the wine is call tannic. White wine tend to have less tannin than red wine.
Tannins are polyphenolic