A blister is collection of fluid underneath the top layer of skin (epidermis). One that is more than 5 mm in diameter with thin walls and is full of watery fluid is called a bulla or a bleb. There are many causes of blisters including burns, vesicant agents, friction forces, and diseases of the skin.
There are a number of types of blisters, including:
- Blood blister -- a blister full of blood due to a pinch, bruise or repeated friction.
- Water blister -- a blister with clear watery contents that is not purulent (does not contain pus) and is not sanguineous (does not contain blood).
- Fever blister -- a blister in the mouth or around it that causes pain, burning, or itching before bursting and crusting over. It is due to the herpes simplex virus which is latent (dormant in the body) and can be reawakened (reactivated) by such factors as stress, sunburn, or fever. Hence, it called a fever blister or a cold sore.
Blisters can form as a reaction to external factors or certain skin diseases, which may include:
- friction (from a shoe, for example)
- eczema (also known as atopic dermatitis)
- impetigo (a contagious infection of the skin)
- phemphigus (a rare, blistering skin disease often occurring in middle-aged and elderly adults)
- pemphigoid (a blistering autoimmune disorder)
- dermatitis herpetiformis (a blistering autoimmune disorder)
- viral infections (including chickenpox and herpes zoster)
The symptoms of a blister may resemble other dermatologic conditions. Consult a physician for diagnosis.
A blister will usually heal on its own. Treatment may include:
- keeping the area clean
- antibiotics (to treat infections)
- dressings on burst blisters