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

Other types of injuries to the skin that may cause a blister 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 develops within a few hours to 3 to 4 days following the bite. This sore may take months to heal.

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

• Chickenpox (varicella) is a common contagious illness that is caused by a type of herpes virus. Chickenpox blisters begin as red bumps that turn into blisters and then scab over. It is most contagious from 2 to 3 days before a rash develops until all the blisters have crusted over.
• Shingles , often seen in older adults, is caused by the same virus that causes chickenpox. Shingles blisters look like chickenpox, but they usually develop in a band on one side of the body.
• Cold sores , sometimes called fever blisters, are clusters of small blisters on the lip and outer edge of the mouth. They are caused by the herpes simplex virus. Cold sore-type blisters that develop in the genital area may be caused by a genital herpes infection.
• Impetigo is a bacterial skin infection. Its blisters, which often occur on the face, 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, which occurs when mites burrow into the skin, may cause tiny, itchy blisters that often occur in a thin line or curved track.
• Bedbugs , which 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. Contact with certain plants, such as poison ivy, oak, and sumac, may occur indirectly.
• Blisters may develop from a disease that causes your body to attack your own skin (autoimmune disease).

Occasionally a prescription or nonprescription medicine or ointment can cause blisters. The blisters may be small or large and usually occur with reddened, itchy skin. If the blisters are not severe and you do not have other symptoms, stopping the use of the medicine or ointment may be all that is needed. Blisters that occur with other signs of illness, such as a fever or chills, may indicate a more serious problem.

Review the Emergencies and Check Your Symptoms sections to determine if and when you need to see a health professional.