A blister is a bubble of fluid under the skin. The clear, watery liquid inside a blister is called serum. It leaks in from neighboring tissues as a reaction to injured skin. If the blister remains unopened, serum can provide natural protection for the skin beneath it. Small blisters are called vesicles. Those larger than half an inch are called bullae. A blood blister is filled with blood, rather than serum.
There are many causes of blisters, including:
In general, blisters are round or oval bubbles of fluid under the skin that may be painful or itchy, or they may not cause any symptoms. Symptoms vary depending on the cause.
If the cause of your blisters is not obvious, your doctor will ask about your family history and your personal medical history, including any allergies you have and any medications you take, including over-the-counter medications. You also will be asked about any recent exposure to irritating chemicals or allergens.
Your doctor often can diagnose the cause of your blisters by their appearance and your history. If your doctor suspects an allergic reaction, he or she may recommend patch tests with chemicals to identify the allergen. Some blistering diseases are diagnosed with a skin biopsy, in which a small piece of tissue is removed and examined in a laboratory.
How long blisters last depends on their cause. For example, blisters caused by irritation generally go away on their own within a few days, and those triggered by infections and skin diseases can remain for weeks or months. With an autoimmune blistering disorder, blistering may be chronic (long-lasting) and requires ongoing treatment. In skin infections, such as herpes simplex virus infection, the blisters can come back periodically. Blistering skin diseases that result from inherited causes also are long-lasting.
There are many simple strategies to prevent blisters caused by skin irritation. You can wear comfortable shoes that fit well, with socks that cushion the feet and absorb sweat. Apply sunscreen to protect your skin from sunburn. Be particularly vigilant about avoiding sun exposure if you are taking medications that are known to cause sun sensitivity, such as doxycycline (sold under many brand names). During cold months, use mittens, hats and heavy socks to protect your skin against freezing temperatures and chilling winds.
As much as possible, avoid irritants and allergens that tend to trigger eczema, such as certain hygiene products (bubble baths, feminine hygiene sprays, detergents), certain metals in jewelry, especially nickel, and irritating plants such as poison ivy.
To prevent blisters caused by infections, wash your hands often and never touch skin sores, cuts or any open or broken areas of skin on other people. To reduce the risk of herpes simplex, never have sex (even with a condom) with someone with active herpes. In addition, the fewer sexual partners you have, the lower your risk of herpes simplex. To avoid the spread of childhood infections, try to prevent children from sharing toys and utensils that have touched another child's mouth.
To prevent chickenpox and to help prevent shingles later, have your child immunized with the varicella vaccine. People who have not had chickenpox should avoid people with chickenpox or shingles until all of the blisters have crusted over. Adults can be vaccinated if they have never had chickenpox, especially if they are at risk of exposure (for example, day-care workers and teachers).
There is no known way to prevent many of the blistering diseases such as the hereditary forms and the autoimmune (bullous) diseases.
Usually, it is best to leave blisters alone. Because blisters protect the underlying skin, breaking blisters open can increase the chance of infection. Protect blisters with a bandage and cover them until they heal on their own. The liquid in the blister will be re-absorbed and the skin will flatten naturally. If a blister breaks, wash the area with soap and water, then apply a bandage. If a blister is very large or painful, your doctor may drain it and apply an antibacterial cream to prevent infection.
The treatment for blisters caused by eczema, infections and other diseases varies. Some cases of eczema can be treated with corticosteroid cream or pills. Herpes simplex infections and shingles (herpes zoster) sometimes are treated with antiviral medications. Antibiotic cream or pills may be given for impetigo. Chickenpox and coxsackievirus generally are left to go away on their own. The itching caused by chickenpox can be relieved with over-the-counter, anti-itch lotions, such as calamine. With medication-related erythema multiforme, the medication must be discontinued immediately. Corticosteroids sometimes may be prescribed.
Pemphigoid and pemphigus are treated with corticosteroids and/or other immunosuppressive agents. Because dermatitis herpetiformis is associated with celiac sprue (a condition that develops as an immune reaction to gluten in the diet), people with dermatitis herpetiformis may benefit from a diet that does not contain any gluten (a substance found in most grains). Porphyria can be treated with regular removal of blood (phlebotomy) or with medications, including cholestyramine (Questran), chloroquine (Aralen) and beta-carotene. Some inherited skin disorders that cause blistering may respond to measures that protect the skin from trauma.
Call your doctor whenever you have blisters of unknown cause, very painful blisters, or blisters accompanied by other symptoms such as fever and malaise (a generally sick feeling). Also call your doctor if a blister develops signs of infection, such as increasing redness, red streaks in nearby skin, oozing blood or pus, increased pain or swelling of the surrounding skin.
In many cases, blisters will disappear when the cause is removed or the infection has gone away, usually in a matter of days or weeks. In most herpes infections, blisters can return in the same spot (such as fever blisters on the lips or genital herpes) weeks, months or even years after the first blisters appear. Pemphigoid and pemphigus are typically chronic (long-lasting) and require long-term therapy.
National Institute of Arthritis and Musculoskeletal and Skin Diseases
National Institutes of Health
1 AMS Circle
Bethesda, MD 20892-3675
Centers for Disease Control and Prevention (CDC)
1600 Clifton Road
Atlanta, GA 30333
American Social Health Association
P.O. Box 13827
Research Triangle Park, NC 27709