Blisters are fluid-filled bumps that look like bubbles on the skin. You may get a blister on your foot when you wear new shoes that rub against your skin. Or you may get one on your hand when you work in the garden without wearing gloves. Home treatment is often all that's needed for this type of blister.

Other types of injuries to the skin can cause a blister. They include:

  • Burns from exposure to heat, electricity, chemicals, radiation from the sun, or friction.
  • Cold injuries from being exposed to cold or freezing temperatures.
  • Some spider bites, such as a bite from a brown recluse spider. Symptoms of a brown recluse spider bite include reddened skin followed by a blister that forms at the bite site, pain and itching, and an open sore with a breakdown of tissue (necrosis) that occurs within a few hours to 3 to 4 days after the bite. This sore may take months to heal.
  • Pinching the skin forcefully, like when a finger gets caught in a drawer. A blood blister may form if tiny blood vessels are damaged.

Infection can cause either a single blister or clusters of blisters.

  • Chickenpox (varicella) is a common contagious illness. It's caused by a type of herpes virus. Chickenpox blisters start as red bumps. They turn into blisters and then scab over. Chickenpox is most contagious from 2 to 3 days before a rash appears until all the blisters have crusted over.
  • Shingles is caused by the same virus that causes chickenpox. It's often seen in older adults. Shingles blisters look like chickenpox. But they usually form in a band on one side of the body.
  • Hand-foot-and-mouth disease is another type of viral infection. It most often occurs in young children. Symptoms include a rash of small sores or blisters that usually appear on the hands and feet and in the mouth.
  • Cold sores are clusters of small blisters on the lip and outer edge of the mouth. They're sometimes called fever blisters. They are caused by the herpes simplex virus. Cold sore-type blisters that form in the genital area may be caused by a genital herpes infection.
  • Impetigo is a bacterial skin infection. Its blisters often occur on the face. They burst and become crusty (honey-colored crusts).
  • Infected hair follicles (folliculitis) cause red, tender areas that turn into blisters at or near the base of strands of hair.
  • A scabies infection occurs when mites burrow into the skin. It may cause tiny, itchy blisters that often form in a thin line or curved track.
  • Bedbugs can cause tiny, itchy blisters anywhere on the body.

Inflammation may cause skin blisters.

  • Contact dermatitis occurs when skin touches something in the environment that causes an allergic reaction.
  • Blisters may form from a disease that causes your body to attack your own skin ( autoimmune disease).

Sometimes a prescription or nonprescription medicine or ointment, such as antibiotics or pain medicine, can cause blisters. The blisters may be small or large. They most often occur with red, itchy skin. If the blisters aren't severe and you don't have other symptoms, stopping the use of the medicine or ointment may be all that's needed. Blisters may also occur as a symptom of a toxic reaction to a medicine. This reaction is called Stevens-Johnson syndrome. Blisters that occur with other signs of illness, such as a fever or chills, may mean a more serious problem.