Tannic Acid in Tea

Do you know if tannic acid is in all teas? I understand that it is tannic acid and not caffeine in tea that is unhealthy for your body. If this is true, can you tell me where I can find more information concerning this?

Tannic acid is not present in most herb teas. It is present in black or Chinese green tea, made with the leaves of Camellia sinensis, and that is probably how you heard about tannic acids in tea.
Tannic acid is of some concern because it is thought to cause cancer when taken over a long time. There is no conclusive proof of this though.
The practice of adding milk to black tea neutralizes the tannic acids. Proteins in milk bind to the tannic acid and make them undigestible and they pass through the body without being absorbed.