A sweater designed to be worn right-side-out and inside-out is reversible. The health effects of a cold are reversible, too. Reversible means able to be undone or able to be used inside-out.
The great thing about reversible clothes is that it's like getting two pieces for the price of one. The great thing about reversible damage is that it can be fixed. Damage that can't be fixed is called irreversible, but t-shirts meant to be worn only one way are simply called t-shirts.