A collection of fluid beneath the outer layer of skin that eventually forms a raised area. The fluid is made up of serum that has leaked from blood vessels in underlying skin layers after major damage. It provides protection for the damaged tissue.
Common causes of blisters are friction and burns. Blisters can also occur in some skin diseases including eczema, erythema, impetigo, epidermolysis, bullosa, multiforme, pemphigus, pemphigoid and dermatitis herpetiformis and in some types of porphyria. Small blisters develop in herpes simplex, herpes zoster (shingles) and chickenpox. Blisters are usually best left intact; unexplained or large blisters need medical attention.