Blisters are pockets of fluid that form in the upper layers of the skin in response to friction, burns, or other types of injury. If a blister is not too painful, it is best to keep it intact to provide a natural barrier against bacteria. For a painful blister, the fluid can be drained while leaving the overlying skin in place using sterilized needles and bandages. Proper footwear and socks can help prevent friction blisters from forming on the feet.