Blisters

What is a blister, and how common is it?

A blister is a small pocket of fluid that forms in the upper layers of damaged skin. It can appear anywhere on the body, but blisters are most common on the hands and feet¹. Most hold clear fluid. Some hold blood (a blood blister), or pus if the blister becomes inflamed or infected¹.

The blisters you get on your feet are usually friction blisters. A friction blister is a tear inside the top layer of skin, and it fills with fluid within about 2 hours². Foot blisters are very common in runners and hikers².

What causes blisters, and who gets them?

Foot friction blisters come from repeated shear: layers of skin sliding against each other as the bones beneath move, with a high friction force, again and again². If you've recently started a lot more walking, running or hiking, or changed your shoes or socks, that's worth thinking about.

Blisters can also come from heat (such as sunburn or a scald), chemicals such as detergent, allergic reactions, and conditions such as chickenpox and impetigo (a bacterial skin infection)¹³.

If you have diabetes, take extra care. Diabetes can reduce feeling and blood flow in the feet, so you may not feel rubbing, pressure or small injuries⁴.

What does a blister feel like, and how is it diagnosed?

A blister usually looks like a reddened, tender patch of skin with a raised lump of clear fluid, or sometimes blood⁵. A podiatrist or doctor will look at it and ask about your activity, shoes and socks, and any recent burns or new products.

An infected blister can be hot and filled with green or yellow pus, with red skin around it. Redness can be harder to see on brown or black skin⁶.

Blisters from a burn, scald, sunburn or allergic reaction, or with no obvious friction cause, should be reviewed by a doctor rather than treated as friction blisters³⁵. Other conditions, such as bullous impetigo and scabies (a skin condition caused by tiny mites), can also cause blisters³.

What helps first?

Care is mostly about protection. Where possible, don't burst a blister or remove its roof, because that can cause infection and slow healing⁵. Keep it covered and away from the shoe or equipment that caused it.

If a blister has already burst, let the fluid drain, then cover it with a clean plaster or dressing. Don't peel or pick at the skin⁶.

If the roof has come off, a podiatrist or doctor may use a sterile, non-stick dressing⁷. Draining a blister is a job for a clinician using sterile instruments, and blisters have different causes, so there's no single right treatment for all of them⁷.

What helps if that isn't enough?

If a blister is large, painful, slow to heal or infected, a podiatrist or doctor can look at it and choose the care that suits the cause⁷. They may drain it with sterile instruments. If it's infected, they may use antimicrobial wound products for a short time⁷.

If you have diabetes, well-fitting shoes that support your feet and avoid pressure points matter a great deal⁴. A podiatrist can check your footwear and help you find a better fit.

How long does it take, and how do I stop it coming back?

How long a blister takes to heal isn't clear. What helps is keeping the roof on, not bursting it, and protecting the spot from more friction while it settles⁵.

If blisters keep coming back, look at your socks and shoes: fit, pressure points and how quickly you've increased your activity. In military recruits, a specially designed boot sock with a liner was linked with fewer blisters than standard socks⁸. This doesn't show the same result for everyone.

If you have diabetes, check your feet every day. A blister that isn't healing can become more serious, so see your podiatrist about it⁹¹⁰.