This is a bubblelike, fluidfilled area on the skin caused by bums, friction, contact with chemicals, or disease. A blister results from an accumulation of fluid beneath the outer layer of the skin (epidermis).
The fluid is composed of sterile, clear serum or blood that has leaked from blood vessels into underlying tissue after injury. The fluid causes the epidermis to become inflamed, although the combination of the fluid and the inflammation protects deeper tissues from further injury.
During healing, new skin forms at the base of the blisters underneath the serum, the serum is reabsorbed and, eventually, the outer layer of skin peels off. Never break a blister; you will increase the risk of infection.