Blisters are accumulations of fluid between two layers of the skin. A lesion smaller than 0.5 centimeters is called a vesicle; when greater than 0.5 centimeters it is called a bulla (plural: bullae).
Blisters are caused by friction, trauma, or internal conditions. Some autoimmune diseases produce blisters when antibodies (immune proteins) attack the cells of the skin. This causes a cleavage between two layers of cells in which fluid accumulates.
Diagnosis of a particular blistering disorder usually is done by biopsy, in which a skin sample is taken from a blister's edge for microscopic evaluation. Sometimes a test called immunofluorescence is performed to look for specific immune proteins that help distinguish one blistering disorder from another.
Some blistering diseases are inherited. These genetic disorders can be diagnosed during pregnancy by chorionic villus sampling.
Treatment for blistering disorders varies with cause and the severity of the disease. Locally administered creams are sometimes effective. In some cases systemic therapy is required.