A blister is a fluid filled lump that appears where the skin's outer layer is repeatedly rubbed or in some other way injured.
Most people have had a blister on their heel from new or uncomfortable shoes. The fluid forms under the damaged skin between the top layer (epidermis) and the bottom layer (dermis) of our skin and fills with plasma which leaks in from the surrounding tissues.
Common causes of blisters include:
- severe sunburn
- burns and scalds
- insect bites or stings
- viral infections of the skin such as cold sores on the lips
- fungal skin infections
- allergic reaction to products or chemicals that come in contact with the skin or medicines taken by mouth
- more common in tropics, sweaty feet, walking or running long distances.
A blister appears as a raised area of skin filled with clear fluid, or occasionally blood. Blisters can be quite tender and hurt if pressed or rubbed. Blisters are classified as 'vesicles' if they are 0.5 cm or less in diameter and as 'bullae' if they are larger.
In most cases, a small blister can be treated at home. Covered with a plaster, it will settle and heal over 3–7 days. Tips for caring for blisters:
- Keep clean and cover with a plaster or soft dressing (if padding is needed to prevent further rubbing or friction).
- Let the blister heal on its own rather than bursting. This reduces the risk of infection.
- If the blister skin lifts, breaks or bursts, gently press to remove any fluid, then wash with warm saline or water, dry and cover.
- If any signs of infection appear, such as redness around the blister, swelling or pus, see your doctor.
To help prevent blisters:
- wear good-fitting, comfortable footwear and socks
- good shoe insoles can help reduce pressure points
- avoid sunburn or any hazards for burns or scalds
- wear gloves to help protect your hands if you are doing repetitive work or sports (working tools, rowing etc).
Seek advice from your doctor, nurse or pharmacist if you have any of the following symptoms:
- The blister is large or multiple blisters have appeared (eg from scald/burns, sunburn, infection).
- If you have blisters and underlying medical conditions such as diabetes or low immunity, or are also unwell for any reason.
- If there are patches or groups of blisters (this could be a viral infection such as shingles, chickenpox).