A blister is a bubble of fluid that forms beneath a thin layer of dead skin. The fluid is a mixture of water and proteins that oozes from injured tissue. Blisters that develop as part of a systemic (bodywide) disease may start in the deeper layers of the skin and cover widespread areas. These blisters heal more slowly and may leave scars.
Many diseases and injuries can cause blistering, but three autoimmune diseases—bullous pemphigoid, dermatitis herpetiformis, and pemphigus vulgaris—are among the most serious.
