What is a blister?
A blister is a small pocket of body fluid within the upper layers of the skin caused by forceful rubbing (friction), excessive heat or cold, chemical exposure or infection. Most blisters are filled with a clear fluid. However, blisters can be filled with blood or with pus if they become infected.

How are blisters treated?

Most small blisters should be covered with a band-aid or other protective bandage. Routine popping or draining of blisters is not necessary in most cases. However, if the blister is large (what doctors call a bulla), then draining the blister will prevent the overlying skin from shearing off and leaving raw skin exposed. To drain a blister, use a sterile pin or knife and make a small hole at the edge of the blister. Drain the fluid from the blister. It’s important to cover the site with a band-aid, bandage, or moleskin to prevent the skin from shearing off.

What can be done to prevent blisters?
The most important factor in preventing blisters is control of friction and moisture. Properly fitted shoes and moisture wicking socks are often adequate. Body Glide () is an effective product that reduces friction in many areas, not just the feet. Anti-perspirant sprays and other powders that reduce moisture can reduce blister formation. Not all blisters are preventable. In such cases, manage them as outlined above.

This information is not intended to diagnose, treat, or prevent any injury or disease. It is intended to serve as an overview of running-related injuries and should not be used as a substitute for sound medical advice from a doctor or therapist.