Drinking tea is both good and bad for you. How can that be? Regular tea boosts the immune system (unlike coffee), but herbal tea contains acids that eat away tooth enamel.
Regular tea contains chemicals called alkylamine antigens, which are also present in some bacteria, cancer cells, parasites and fungi. When the body is exposed to them through tea drinking, it can build up a defense against them and will be more able to fight them off. Green and black teas contain the antigens, but coffee does not.