Blister

A collection of fluid beneath the outer layer of the skin that forms a raised area. A blister contains fluid that has leaked from blood vessels in underlying skin layers after minor damage and protects the damaged tissue. Common causes are burns and friction. Blisters may also occur with pemphigus, pemphigoid, dermatitis herpetiformis, some types of porphyria, and some skin diseases. These include eczema, epidermolysis bullosa, impetigo, and erythema multiforme. Small blisters develop in the viral infections chickenpox, herpes zoster (shingles), and herpes simplex. Generally, blisters are best left intact, but large or unexplained blisters need medical attention.