A blister is a soft area of skin filled with a clear fluid. Blisters may form in response to heat in the case of a burn or an irritant in the case of a chemical. Frequently, the blister is caused from friction, such as a coarse fabric rubbing repeatedly against a person’s skin. In other cases, blisters form in response to a chemical or allergic irritant, which is known as contact dermatitis. Some oral and topical drugs may cause blisters to appear. Blisters can also be symptomatic of bacterial or viral skin infections, such as chicken pox, shingles, impetigo or ringworm.

Most blisters do not require medical attention. The most important information to remember is not to rupture break open a blister. A blister acts as a protective covering for damaged skin and helps prevent infection. If a blister does open on its own, be sure to leave the covering in place to support further healing. Simply wash the area gently with mild soap and water, pat it dry and apply petroleum jelly. Cover the blister with bandage to keep it clean. Replace the dressing at least once a day. Watch for signs of infection, such as a white or yellow pus coming from the blister, redness or red streaks around the blister or an increase in skin temperature around the blister.

To avoid blisters, you need to eliminate the irritant. Some simple ways to avoid blisters are to avoid tight clothing, make sure socks and shoes fit properly, and when doing heavy work with your hands, wear work gloves.

There are categories of "blistering diseases" such as pemphigoid and pemphigus, but these diseases usually present dramatically with multiple blisters, many of them large and erosions in the mouth and other surfaces.