A blister is a pocket of fluid in the upper layers of the skin, commonly caused by repeated rubbing or burning. Most blisters should not be burst or popped but, rather, left to heal on their own. However, blisters that become infected, or that are caused by an underlying medical condition, may require treatment.
Blisters are one of the body’s responses to injury, friction, or an underlying medical condition. The damaged upper layer of skin (epidermis) tears or peels away from the layers beneath. A clear fluid (serum) then collects in the space to create a blister to protect the underlying layers and promote its repair. If a blood vessel in the skin is damaged, the blister is filled with blood rather than serum and forms a blood blister.
Blisters are also referred to as vesicles (usually for smaller blisters) and bullae (for larger blisters).
Most blisters are caused by friction, i.e. when the skin is repeatedly rubbed for a long period of time or when it is subjected to intense rubbing over shorter periods. Friction blisters most commonly occur on the feet and hands when they rub against footwear and handheld equipment such as tools or sports gear.
Blisters can also develop when the skin is exposed to excessive heat (e.g. sunburn or boiling water), freezing cold (e.g. frostbite), or irritating chemicals or substances (e.g. detergents, solvents). They can also develop due to an allergic reaction, including in response to an insect bite or sting.
Blisters can also be caused by certain medical conditions, including:
- Cold sores
- Genital herpes
- School sores (impetigo)
- Hand foot and mouth disease
- Diabetes (in a very small proportion of cases)
- Autoimmune blistering disorders (such as bullous pemphigoid).
In addition, some types of medication can cause mild blistering skin reactions while other types of medication can increase the risk of blistering due to sunburn by increasing the skin’s sensitivity to sunlight.
Signs and symptoms
Specific symptoms tend to vary depending on the cause. For example, blisters caused by friction or burns are usually painful while blisters resulting from eczema may be accompanied by redness, itching, and small bumps on the affected skin.
In general, blisters are round or oval bubbles of clear serum under the skin that may be painful or itchy, or they may not produce any symptoms. Blood blisters are red or black and filled with blood instead of serum.
Infected blisters are red, hot, and filled with green or yellow pus. An infected blister should not be ignored. Without treatment, an infected blister can lead to a skin infection (including impetigo), cellulitis, or even a blood infection (sepsis).
Friction blisters are easily self-diagnosed. If the cause of your blisters is not obvious, your GP can diagnose the cause by the appearance of the blister and your personal and family medical history, including any allergies you have and any medications you have taken. Your GP may also ask about any recent exposure to irritating chemicals or allergens.
If your GP suspects an allergic reaction, they may recommend patch tests to identify the allergen. Some blistering diseases are diagnosed with a skin biopsy, which involves a small piece of tissue being taken and examined in a laboratory.
It is usually best not to burst a blister, and to leave them alone. Blisters themselves should be protected with a plaster or other sterile dressing and kept covered until they have healed.
Bursting a blister increases the risk of it becoming infected and may hinder the healing process.
Friction blisters heal within a week and don’t usually require medical attention unless they are severe, recurrent, or occur in people who have circulation problems or diabetes .
Self-care measures for blisters include:
- Applying an ice pack wrapped in a tea-towel to a blister to help to relieve any pain.
- Covering a blister with a soft plaster or dressing, especially if it is likely to burst.
- Not breaking or popping a blister yourself.
- Washing your hands before touching a burst blister.
- Allowing the fluid in a burst blister to drain before covering it with a sterile dressing.
- Not peeling the skin off a burst blister or picking at the edges of any remaining skin. (the skin covering the blister helps to protect it from infection)
- Not wearing the shoes or using the equipment that caused the blister until it has healed.
However, you should see a GP if:
- You think a blister is infected.
- A blister is extremely painful or keeps coming back.
- A blister is in an unusual place, e.g. eyelids, mouth, or genitals
- Several blisters have appeared for no apparent reason
- A blister was caused by a burn or scald, sunburn, an allergic reaction, or chemicals or other substances.
Your GP might burst a large or painful blister under sterile conditions. If a blister is infected, they may prescribe antibiotics.
A pharmacist can recommend a suitable plaster or dressing to protect your blister from becoming infected while it heals.
Blisters caused by a medical condition, such as chickenpox, genital herpes, diabetes or impetigo should be seen by a GP who will be able to treat the blister and advise on managing the underlying condition.
Taking the following precautions will help to minimise the chances of developing blisters caused by friction:
- Wear comfortable shoes that fit properly.
- Break new shoes in gradually.
- Keep feet as dry as possible and dust talcum powder into your socks.
- Wear thicker sports or wool socks when exercising or playing sports.
- Lubricate friction areas in new sports shoes/boots (such as around the heel) with petroleum jelly.
- Wear protective gloves when gardening or using tools at work.
- If you feel a localised friction spot on a hand or foot during sport or other physical activity, immediately stop and apply protection such as plasters or tape to the area.
If you are especially susceptible to friction blisters, it may be worthwhile visiting a podiatrist (someone who diagnoses and treats foot disorders). They are able to advise on appropriate footwear, protective dressings, and other prevention measures.
Precautions should also be taken to prevent blisters from other causes:
- Before going out in the sun, apply sunscreen, keep skin covered, and wear a sun hat.
- Take care around household sources of heat such as ovens, hot water jugs, and heaters.
- Use appropriate safety equipment when working in environments involving heat or chemicals.
- Wear protective gloves (and eye protection) when using harsh detergents, cleaning products, solvents, and other chemicals.
- Avoid as much as possible, irritants and allergens that can trigger eczema.
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Mayo Clinic (2018). Blisters: First aid (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/first-aid/first-aid-blisters/basics/art-20056691 [Accessed: 10/10/18]
MedlinePlus (2016). Blisters (Web Page). Bethesda, MD: US National Library of Medicine (NIH). https://medlineplus.gov/blisters.html [Accessed: 10/10/18]
NHS (2017). Blisters (Web Page). Redditch: National Health Service (NHS)
England. https://www.nhs.uk/conditions/blisters/ [Accessed: 10/10/18]
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Created: October 2018