Single blisters that everyone suffers from are usually caused by friction when something rubs against the skin. Bad-fitting shoes are a common example of this. Any kind of burn, including sunburn, may cause blisters too.

Certain medical complaints cause blisters to appear on different parts of the body. These include eczema, chickenpox and the bacterial infection impetigo, where the blisters may be filled with pus rather than the usual clear fluids.

Blisters can also form as a reaction to certain medications including some antibiotics, and there are a number of rarer blistering skin conditions, some of which are caused by an autoimmune reaction, where the body’s immune system attacks cells in the skin.

A blister is formed when fluid from blood vessels leaks into the skin. It then collects beneath the outer layer of skin forming the typical raised bump.

As new skin grows beneath the blister, the fluid contained within it is slowly absorbed, and the skin on top dries and peels off. The blister heals naturally without any treatment.

Never burst a blister to release the fluid because the skin acts as a barrier against infection. When the skin of the blister breaks of its own accord, or as a result of minor trauma, cover it with a sterile, dry dressing to protect the area from infection until it has healed.

If the blister becomes red, hot, filled with pus, or painful then seek medical advice because you may need treatment for possible infection.

This article was last medically reviewed by Dr Trisha Macnair in November 2007