What is a blister?

A lump filled with fluid appears when the skin's outer layer is injured. This fluid sac, called a blister, forms under the damaged skin and protects the sensitive new skin growing underneath it. While the new skin grows, the body gradually reabsorbs the fluid. The process usually takes 3-7 days. Sometimes, the blister breaks on its own. If the blister is more than 5 mm in diameter with thin walls and is full of fluid it can also be called a bulla or bleb.

Types of blisters

Blood blister — a blister that is full of blood. Often caused by a pinch to the skin, bruising or repeated friction on an area.

Fever blister — a blister that occurs in or around the mouth that causes pain, burning or itching before bursting and forming a crust. It is caused by the herpes simplex virus and is generally called a cold sore.

Water blister — the most common form of blister. It is filled with a clear watery fluid that does not contain pus from an infection and does not contain blood.

What are the symptoms of blisters?

• A raised and tender area of skin filled with clear fluid.
• Pain on pressure.

Common causes of blisters

• Friction.
• Allergic reaction to chemicals that come in contact with the skin.
• Burns, scalds.
• Sunburn.
• Insect bites or stings.
• Viral infection of the skin.
• Fungal infection of the skin.

What you can do

• Do not burst the blister. Let it heal on its own to avoid infection.
• Keep the blister and surrounding area clean.
• Cover the blister with a soft dressing if it is in an area that may get bumped or rubbed during the day.
• If the blister breaks, press the area to get rid of all the fluid. Then, wash it with mild soap and warm water, or paint it with an antiseptic. Repeat the procedure twice a day to prevent infection.
• Consult a doctor if there is an increase in redness around the blister, swelling, or pus as these are signs of infection.

What your doctor can do for you

• If the blister becomes infected, it may require the following medical treatment.
• Drainage of the pus or fluid under sterile conditions and application of suitable treatment and dressing.
• Antibiotics if bacterial infection is present.
• Treatment of any allergy that may be present.

Preventing blisters

• Establish the causes of your skin allergy and avoid them as much as possible.
• Wear good-fitting, comfortable footwear and socks.
• Wear gloves if your working tools cause a lot of friction.

Original material provided by myDr, October 2004. Edited by everybody, July 2005.