Blisters are caused by several things:

Friction: Blisters can develop when a surface rubs against exposed skin, such as a tool handle against the hand or a new pair of shoes against the ankle. Unlike corns and calluses, which develop from prolonged rubbing, friction blisters come from brief, intense rubbing on a small area.

Burns: Flames, steam, or contact with a hot surface can cause blisters, as can severe sunburn or exposure to other types of radiation.

Cold: Exposure to extreme cold may rarely cause blistering. For example, when a wart is frozen off, a blister will result.      

Contact with irritants or allergens: Skin may blister when it comes in contact with chemical irritants, cosmetics, and many plant allergens. This is called irritant or allergic contact dermatitis.

Drug reactions: Many people develop blisters as a reaction to taking certain drugs. Before prescribing any new drugs, a doctor should ask about any drug reactions you may have had in the past. If you develop a blister while on medication, call your doctor.

Autoimmune diseases: Of the various autoimmune diseases known to cause blistering, three are most common.

• Pemphigus vulgaris, a potentially fatal skin disorder, causes blisters in the mouth or skin; these painful blisters become raw and crusted after bursting.
• Bullous pemphigoid causes less severe eruptions that heal faster and are not life-threatening; this condition is seen chiefly in the elderly.
• Dermatitis herpetiformis causes small, itchy blisters; it is a chronic condition that usually starts in early adulthood.

Infection: Blisters are a common symptom of many infectious illnesses, including chickenpox, cold sores, shingles, and a skin infection called impetigo.

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