Blisters

A blister is a pocket of fluid beneath the outer layer of skin. Most form when skin is damaged by rubbing, heat, cold, chemicals, or irritation.

The fluid is usually clear. It cushions the tissue underneath while the skin heals. A blood blister contains blood because small blood vessels have also been damaged. Blisters filled with cloudy or yellow fluid may be infected, although appearance alone cannot confirm this.

Many blisters are minor and heal with protection from further damage. Others can be related to an infection, an ongoing skin condition, a medicine, or a deeper burn. The location, number of blisters, and other symptoms help narrow down the cause.

A blister often looks like a raised bubble with clear fluid inside. The skin around it may be red, tender, itchy, or sore. Friction blisters commonly appear on the heels, toes, palms, or fingers.

A blister may remain intact or break open and leak. The exposed skin underneath can feel raw and painful. Larger blisters are sometimes called bullae, while very small ones are called vesicles.

Other features may include:

• Several small blisters grouped together
• Crusting after a blister breaks
• Blood instead of clear fluid
• Blisters inside the mouth or on the lips
• A rash, fever, pain, or swelling elsewhere

These differences can matter because not all blisters have the same cause.

Friction is a frequent cause. Repeated rubbing from shoes, tools, sports equipment, or damp clothing separates layers of skin. Heat and moisture make this more likely.

Minor burns and sunburn can also cause blisters. The heat damages deeper parts of the skin, allowing fluid to collect. Cold injuries and contact with some chemicals can have a similar effect.

Skin irritation or allergy may cause itchy blisters after contact with substances such as poison ivy, nickel, cosmetics, detergents, or adhesives. This is called contact dermatitis.

Infections can produce single blisters or groups of them. Examples include cold sores, shingles, chickenpox, hand, foot and mouth disease, and some bacterial skin infections. The pattern and accompanying symptoms differ between infections.

Ongoing skin conditions such as eczema can cause repeated small, itchy blisters. Less commonly, immune system conditions make the body attack structures that hold skin layers together, leading to widespread or recurring blisters.

Some medicines can cause blistering reactions. Most medicine rashes are not severe, but widespread blisters, peeling skin, or painful sores in the mouth, eyes, or genitals need urgent assessment.

Seek emergency help if blisters occur with trouble breathing, swelling of the face or throat, faintness, or signs of a severe allergic reaction.

Emergency assessment is also appropriate for rapidly spreading blisters with peeling skin, especially when there are painful sores in the mouth, eyes, or genitals. This is particularly important after starting a new medicine.

Get same-day medical care if:

• Redness, warmth, swelling, or pain is spreading
• Pus, red streaks, fever, or chills develop
• A blister affects the eye or nearby skin
• Pain is severe or the area becomes numb
• A burn is deep, large, chemical, electrical, or on the face or genitals

Arrange a routine appointment if blisters keep returning, appear without an obvious injury, cover several areas, or have not improved after about two weeks. Also seek advice sooner for a foot blister if you have diabetes, reduced feeling, poor circulation, or a weakened immune system.

A healthcare professional will ask when the blisters appeared and whether there was rubbing, a burn, a new skin product, an illness, or a recently started medicine. They may ask about itching, pain, fever, and whether anyone nearby has similar symptoms.

The appearance and distribution often provide useful clues. The skin, mouth, eyes, and nails may be checked when relevant.

Testing is not always needed. When the cause is uncertain, a clinician may take a swab for infection, test a small skin sample, or arrange blood tests. Allergy patch testing may be useful when contact dermatitis is suspected.

For a small friction blister, stop or reduce the activity causing the rubbing. Keep the area clean and cover it with a soft, cushioned dressing. Better-fitting shoes, dry socks, gloves, or padding may help prevent more damage.

Try not to deliberately pop an intact blister. Its covering helps protect the raw skin below from bacteria. If it breaks by itself, gently wash the area with soap and water. Leave the skin covering in place, apply a thin layer of petroleum jelly, and use a clean non-stick dressing. Replace the dressing if it becomes wet or dirty.

A healthcare professional may drain a large or very painful blister using sterile equipment while preserving the skin covering. Avoid draining it yourself if it may be infected or if you have diabetes, poor circulation, or reduced sensation.

For a recent minor burn, cool the area under cool or lukewarm running water for 20 minutes. Do not use ice, butter, or greasy creams. Remove nearby jewellery or clothing unless it is stuck to the skin, then cover the burn loosely with a clean, non-fluffy dressing.

Treatment for other causes is specific to the condition. It may include antiviral medicine, antibiotics like amoxicillin or doxycycline for a confirmed bacterial infection, or treatment to reduce inflammation. Do not stop a prescribed medicine without medical advice unless emergency services tell you to do so.

A minor friction blister often improves within several days and heals within one or two weeks. Deeper burns, infected blisters, and blisters caused by skin conditions may take longer.

The fluid is usually reabsorbed as new skin forms underneath. The loose covering then dries and comes away naturally. Avoid pulling it off early.

Some blisters leave temporary redness or darker skin. Scarring is uncommon after a shallow blister but is more likely after a deep burn, infection, or repeated injury.

Should I pop a blister?

Usually not. Keeping it intact lowers the chance of contamination and protects the tender skin underneath. A clinician can safely drain a large, tense, or painful blister when needed.

Are blisters contagious?

The blister itself is not contagious, but its cause may be. Viral infections such as cold sores, chickenpox, and shingles can spread under certain conditions. Avoid sharing towels or personal items when an infection is possible.

What does a blood blister mean?

A blood blister usually follows pinching, pressure, or friction that damages small blood vessels. Protect it as you would a clear blister. Seek care if it appeared without an injury, is very painful, or does not heal.

Can I exercise with a blister?

You may be able to continue if the blister is small, protected, and not painful. Stop if activity increases pain, rubbing, or leakage. Continuing to apply pressure can enlarge the injury and delay healing.

Why do my blisters keep returning?

Repeated friction is one possibility, but recurring blisters can also be linked to eczema, allergy, infection, or an immune system condition. A routine medical review can help identify the pattern.