A blister, also known as a bulla, is a bubble of fluid that forms beneath a thin layer of damaged skin. The fluid inside is composed of water and protein that have oozed from the damaged tissue. Commonly, blisters form as a result of irritation caused by rubbing, such as that caused by ill-fitting or new shoes. They generally involve only epidermis, the top layer of the skin. Blisters such as these usually resolve on their own fairly quickly, and do not lead to complications or scarring. Blisters may, however, development for a number of other reasons, some of which can be more serious. All blisters should be watched because even seemingly innocuous blisters can become infected easily.

Causes of Blisters

Although most blisters result from irritation of, or pressure on, the skin, there are several types of blisters caused by different injuries or diseases that may be more serious.

Blisters from Injuries

Apart from the usual friction blisters, which can result from a shoe rubbing against a toe, other injuries that cause blisters include:

  • Burns due to exposure to heat, sunlight, electricity, or chemicals
  • Frostbite
  • Pinches due to skin being caught, as in a hinge

A blood blister may occur if small blood vessels are pinched or suffer a traumatic blow, as from a hammer.

Blisters from Disease

Various bacterial or viral infections can cause a single blister or a cluster of blisters to develop. Herpes is often the culprit in such outbreaks of blisters, which may appear as cold sores, genital herpes, chickenpox, or shingles. Other infections that may cause blisters include:

  • Hand-foot-and-mouth disease
  • Impetigo, a bacterial skin infection
  • Folliculitis, infected hair follicles

Blisters from Insects and Arachnids

Several small creatures are capable of causing blisters on humans. Bedbugs are miniscule insects that can cause tiny blisters anywhere on the body. Mites and brown recluse spiders are two types of arachnids that can also cause blisters. The bite of the brown recluse spider is the most dangerous of the three because it results not only in itching and pain but the necrosis (death) of tissue at the site and can take months to heal.

Blisters may also be the result of a severe allergic reaction to a substance in the environment, a toxic reaction to a medication, or a consequence of an autoimmune disease. Any blister, regardless of cause, that becomes increasing swollen, red, hot or painful, or is oozing pus, requires medical evaluation.

Treatment of Blisters

Common blisters, caused by irritation or sunburn, normally heal on their own. The skin that covers them provides a useful protection against potential infection, so they are best left alone. Blisters that occur with signs of illness, such as chills or fever, or with signs of severe allergic reaction, require medical consultation. Large blisters may also necessitate a visit to the doctor.

When small blisters not associated with illness are especially painful, interfering with walking or other daily activities, they may be punctured and drained at home as long as special care is taken to sterilize the needle and antibiotic ointment is applied immediately after the procedure.

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