May also be called: Vesicles; Bullae; Blebs

A blister is an area of raised skin with a watery liquid inside. Doctors may use the terms "vesicles" or "bullae" based on a blister's size. Vesicles (VEH-sih-kuls) are blisters that are smaller than a dime in diameter; bullae (BULL-ay) are those that are larger than a dime.

More to Know

Blisters happen when the upper layers of skin are damaged, leaving a space between the outermost layer of skin (epidermis) and the layers underneath. The space fills with a fluid that is usually clear, although sometimes a blister can fill with blood (this is called a blood blister) or with pus if the blister becomes infected. The fluid cushions and protects the tissue beneath the blister while it heals.

Blisters are often caused by friction (when two surfaces rub against each other). Uncomfortable or poor-fitting shoes can cause blisters on the feet. Blisters can form on the hands from holding something with a lot of pressure, like using a hammer or riding a bike without protective gloves. Other causes of blisters include burns, insect bites, allergic reactions, exposure to certain chemicals, viral infections like chickenpox or herpes, bacterial infections like impetigo, certain skin diseases, and contact with things like poison ivy or poison oak.

The best way to deal with blisters is to avoid getting them in the first place. Making sure shoes fit correctly and wearing the right kind of gloves or protective gear on the hands can prevent many blisters.

Keep in Mind

Blisters can be painful, but usually heal on their own. To care for a blister, keep it clean and dry, covered with a bandage until it goes away. While it heals, try to avoid putting pressure on the area or rubbing it. It's best not to puncture a blister, as this can give bacteria and viruses a way into the body and increase the risk of infection.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.