A blister is a swelling filled with serum or blood formed between two layers of skin following burns, friction, or contact with certain corrosive chemicals (vesicants). Blisters also occur in certain skin diseases.
Most blisters heal naturally and don't need medical attention. As new skin grows beneath the blister, the fluid in the blister is slowly reabsorbed by the body and the skin on top dries and peels off.
The skin over a blister provides a natural barrier to infection and should be left intact until it breaks on its own once the skin underneath has healed.
Small blisters may be covered with a plaster. Larger blisters should be covered with a gauze pad or dressing that can be taped in place. A blister that is painful or in a position that makes it likely to burst (such as on the sole of your foot), should be covered with a soft dressing to cushion and protect it.
If a blister bursts, the dead skin on top should not be peeled. After the fluid inside has drained, the blister and the area around it should be covered with a dry, sterile dressing to protect it from infection until it heals.