Blisters are small pockets of fluid that usually form in the upper layers of skin after it’s been damaged. Blisters can develop anywhere on the body but are most common on the hands and feet.
Fluid collects under the damaged skin, cushioning the tissue underneath. This protects the tissue from further damage and allows it to heal.
Most blisters are filled with a clear fluid (serum), but may be filled with blood (blood blisters) or pus if they become inflamed or infected.
Most blisters heal naturally after three to seven days and don’t require medical attention.
It’s important to avoid bursting the blister, because this could lead to an infection or slow down the healing process.
If the blister does burst, don’t peel off the dead skin. Instead, allow the fluid inside the blister to drain and cover the area with a dry, sterile dressing to protect it from infection until it heals.
Read more about treating blisters.
When to see your GP
See your GP if you have blisters that:
- you think are infected
- are very painful
- keep coming back
An infected blister will be filled with yellow or green pus and may be painful, red and hot.
You should also talk to your GP if you have blisters in unusual places, such as on your eyelids or inside your mouth, or if they appear after severe sunburn, burns or scalds or an allergic reaction, or after coming into contact with chemicals or other substances.
What causes blisters?
Blisters can be caused by:
- friction to the skin
- heat – for example, from sunburn or a scald
- contact with chemicals, such as detergent
- medical conditions, such as chickenpox and impetigo
Read more about what causes blisters.
There are a number of things you can do to avoid getting blisters caused by friction, sunburn or chemicals. For example, you can:
- wear comfortable, well-fitting shoes
- help keep your feet dry with thicker socks or talcum powder
- wear gloves when handling chemicals
- use sunscreen
Read more about preventing blisters.
Causes of blisters
Blisters are most often caused by skin being damaged by friction or heat. Certain medical conditions also cause blisters to appear.
The damaged upper layer of skin (epidermis) tears away from the layers beneath and fluid (serum) collects in the space to create a blister.
Friction blisters are common in people who are very active, such as sports players and those in the military. They’re usually caused by poor-fitting shoes.
A blister can develop if the skin is rubbed for a long period or if there’s intense rubbing over shorter periods.
Friction blisters often occur on the feet and hands, which can rub against shoes and handheld equipment, such as tools or sports equipment. Blisters also form more easily on moist skin and are more likely to occur in warm conditions.
Blisters can appear when skin is exposed to excessive heat – for example, when you have sunburn.
Blisters can sometimes form when your skin comes into contact with substances such as cosmetics, detergents and solvents.
Read about burns and scalds.
They can also develop as an allergic reaction to an insect bite or sting.
A number of medical conditions may cause blisters. The most common are:
- chickenpox – a childhood illness that causes itchy red spots
- cold sores – small blisters that develop on the lips or around the mouth, caused by a virus
- herpes – a sexually transmitted infection (STI) that most commonly affects the groin
- impetigo – a contagious bacterial skin infection
- pompholyx – a type of eczema
- scabies – a skin condition, caused by tiny mites, which may lead to blisters developing on young children’s feet or palms of their hands
- hand, foot and mouth disease – a viral infection that usually affects young children
Several rarer conditions can also cause blisters. They are:
- bullous pemphigoid – a skin disease that causes large blisters and usually affects people over 60 years of age
- pemphigus vulgaris – a serious skin condition where blisters develop if pressure is applied to the skin; the blisters burst easily, leaving raw areas that can become infected
- dermatitis herpetiformis – a skin condition that causes intensely itchy blisters, usually on the elbows, knees, back and buttocks; blisters usually develop in patches of the same shape and size on both sides of the body
- epidermolysis bullosa – a group of rare inherited skin disorders that cause the skin to become very fragile; any trauma or friction to the skin can cause painful blisters
- chronic bullous dermatosis of childhood – a condition that causes clusters of blisters to develop on the face, mouth or genitals
- bullous ichthyosiform erythroderma – a type of icthyosis someone is born with, which causes inflamed, scaly skin with blisters
Most blisters heal naturally and don’t require medical attention.
As new skin grows underneath the blister, your body slowly reabsorbs the fluid in the blister and the skin on top will dry and peel off.
When to seek medical help
See your GP if you have blisters that:
- you think are infected – an infected blister will be filled with yellow or green pus and may be painful, red and hot
- are very painful
- keep coming back
- are in unusual places, such as on your eyelids or inside your mouth
- are caused by severe sunburn, burns or scalds or an allergic reaction
Antibiotics may be prescribed to treat an infected blister.
If you have a large or painful blister, your GP may decide to decompress the blister under sterile conditions.
The unbroken skin over a blister provides a natural barrier to infection. It’s important that the skin remains intact to avoid infection.
As tempting as it may be, try not to pierce a blister with a needle because it could lead to an infection or slow down the healing process. Allow the skin to peel off on its own after the skin beneath has healed.
You may choose to cover small blisters with a plaster. Larger blisters can be covered with a gauze pad or dressing that can be taped in place.
Painful blisters, or those in positions where they’re likely to burst, such as on the sole of your foot, can be covered with a soft dressing to cushion and protect them. It may help to cut the dressing into a ‘doughnut’ shape to fit around the blister and avoid placing pressure directly on it.
Change the dressing daily and wash your hands before touching the blister to avoid infection.
If a blister has burst, don’t peel off the dead skin on top of the blister. Allow the fluid inside to drain and wash it with mild soap and water. Cover the blister and the area around it with a dry, sterile dressing to protect it from infection until it heals.
Hydrocolloid dressings, available over the counter from pharmacies, have been shown to help prevent discomfort and encourage healing.
If the top layer of dead skin from a burst blister has already rubbed off, don’t pick at the edges of the remaining skin. Follow the advice above to protect it from infection.
If the blister is on your foot, avoid wearing the shoes that caused it, at least until it heals.
Read more about applying plasters and other dressings.
Blood blisters should be left to heal naturally. If a blood blister bursts, keep the area clean and dry. Protect it with a sterile dressing to prevent infection.
Blood blisters are often painful. Applying an ice pack to the affected area immediately after the injury can help relieve the pain (a bag of frozen vegetables works just as well). Between 10 and 30 minutes should help.
To stop the ice touching your skin directly, place a towel over the affected area before applying the ice pack.
There are several ways to prevent getting blisters from friction, sunburn or chemicals.
Blisters caused by a medical condition often can’t be prevented and need to be treated by a GP.
Wearing comfortable, well-fitting shoes and clean socks helps prevent blisters.
Blisters are more likely to develop on moist skin. If you have sweaty feet, wearing moisture-absorbing socks or changing your socks twice a day can help prevent them.
If you play sport or exercise regularly, wearing sports socks or thicker wool socks can help keep your feet dry and reduce your risk of getting a blister. Dusting the inside of your socks with talcum powder may also help.
If you’re going for a long walk, wear comfortable shoes that fit properly. Brand new shoes that aren’t broken in may not be comfortable and may rub.
Stop immediately if you feel a hot area on your foot while walking, exercising or playing sport. If possible, tape some padding over the area.
Wear protective gloves when using tools such as shovels or pickaxes, and when doing manual work such as gardening. This will help prevent blisters developing on your hands.
Heat and sunburn
Be careful when dealing with heat such as steam, flames or boiling water. Make sure you use the right safety equipment in working environments involving heat or chemicals.
Moisturiser, aftersun or calamine lotion can help ease discomfort if you do get sunburnt.
Always wear protective gloves when handling detergents, cleaning products, solvents and other chemicals.
Blisters from friction or heat usually have an obvious cause, such as sunburn, wearing shoes that rub or heavy manual work.
Blisters are easy to recognise as raised pockets of skin that contain fluid. Blood blisters are usually red or a darker colour.
Blisters that develop without apparent injury to the skin from heat or friction may be the result of a medical condition. If you develop blisters and you’re not sure why, see your GP. They will be able to investigate what’s causing them.