Blisters are fluid-filled sacs on the outer layer of your skin. They form because of rubbing, heat, or diseases of the skin. They are most common on your hands and feet.
Other names for blisters are vesicles (usually for smaller blisters) and bulla (for larger blisters).
Blisters often happen when there is friction – rubbing or pressure – on one spot. For example, if your shoes don’t fit quite right and they keep rubbing part of your foot. Or if you don’t wear gloves when you rake leaves and the handle keeps rubbing against your hand.
Other causes of blisters include
Poison ivy, oak, and sumac
Autoimmune diseases such as pemphigus
Epidermolysis bullosa, an illness that causes the skin to be fragile
Viral infections such as varicella-zoster (which causes chickenpox and shingles) and herpes simplex (which causes cold sores)
Skin infections including impetigo
Blisters will usually heal on their own. The skin over the blister helps keep out infections. You can put a bandage on the blister to keep it clean. Make sure that there is no more rubbing or friction on the blister.
You should contact your health care provider if
The blister looks infected – if it is draining pus, or the area around the blister is red, swollen, warm, or very painful
You have a fever
You have several blisters, especially if you cannot figure out what is causing them
You have health problems such as circulation problems or diabetes
Normally you don’t want to drain a blister, because of the risk of infection. But if a blister is large, painful, or looks like it will pop on its own, you can drain the fluid.
Courtesy of MedlinePlus from the National Library of Medicine