A blister is a raised pocket of fluid within the upper layers of the skin. This fluid, typically clear serum, accumulates as a response to skin injury, providing a natural protective cushion for the underlying tissue. Smaller blisters are often referred to as vesicles, while larger ones, exceeding half an inch in diameter, are known as bullae. A blood blister occurs when the pocket fills with blood instead of serum. Understanding “What Is A Blister” involves recognizing its diverse causes and appropriate management.
Blister on a foot due to friction
Causes of Blisters
Blisters arise from various factors, which can be broadly categorized as follows:
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Irritation: Physical irritants like friction (e.g., shoes rubbing against the skin), exposure to harsh chemicals, or extreme temperatures (both hot and cold) can trigger blister formation. Contact dermatitis, a skin reaction to chemical irritants, also falls under this category. Frostbite, resulting from intense cold, often leads to blisters upon rewarming the skin. Burns, including sunburns, are common culprits as well.
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Allergies: Allergic contact dermatitis, a type of eczema, can manifest as blisters. Common allergens include poison ivy, poison oak, and poison sumac. The body’s immune response to these substances leads to inflammation and blister development.
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Infections: Several infections can cause blisters. Bullous impetigo, a bacterial skin infection caused by staphylococci, is one example. Viral infections like herpes simplex (types 1 and 2), responsible for cold sores and genital herpes, respectively, also cause blisters. Chickenpox and shingles, both caused by the varicella-zoster virus, and coxsackievirus infections, frequently seen in children, are additional infectious causes.
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Skin Diseases: Numerous skin conditions are associated with blister formation. These include dermatitis herpetiformis, pemphigoid, and pemphigus. Inherited conditions like epidermolysis bullosa, where minor trauma leads to blistering, and porphyria cutanea tarda, where sun exposure triggers blisters, also fall into this category.
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Medications: Certain medications can induce blistering skin reactions. Some drugs, such as nalidixic acid and furosemide, may cause mild blistering. Others, like doxycycline, can increase the skin’s sensitivity to sunlight, raising the risk of blistering sunburns. In rare but severe cases, medications can trigger life-threatening blistering disorders like erythema multiforme or toxic epidermal necrolysis (TEN), characterized by extensive skin damage.
Symptoms of Blisters
Blisters typically appear as round or oval fluid-filled pockets beneath the skin. They may be painful, itchy, or cause no symptoms at all, depending on the underlying cause.
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Irritation, Burns, and Allergies: Blisters caused by friction or burns tend to be painful. Eczema-related blisters may be accompanied by redness, intense itching, and small bumps on the affected skin.
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Infections: Symptoms vary depending on the specific infection:
- Bullous Impetigo: Affected skin may be red, and blisters may rupture easily.
- Herpes Simplex Virus: Type 1 causes fever blisters or cold sores, typically on the lips. Prior to blister formation, the affected skin may itch, tingle, swell, and become red. Upon rupture, blisters release fluid and develop into painful sores. Type 2 is the primary cause of genital herpes, characterized by small red bumps preceding blister development in the genital area, buttocks, thighs, or anus. Other symptoms may include fever, muscle aches, headache, and burning during urination.
- Varicella-Zoster Virus: Chickenpox begins with a widespread, itchy rash that rapidly progresses into itchy blisters. Shingles (herpes zoster) manifests as small, painful blisters that typically follow a linear pattern along an infected nerve.
- Coxsackievirus: Coxsackievirus A16 can cause hand-foot-and-mouth disease, characterized by painful blisters on the hands, soles of the feet, and in the mouth.
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Skin Diseases: Erythema multiforme often causes blisters on the palms, forearms, soles, and mucous membranes of the eyes, nose, mouth, and genitals, accompanied by fever, sore throat, cough, and muscle pain. Autoimmune diseases, also known as bullous diseases, exhibit varying appearances. Dermatitis herpetiformis causes itchy, red bumps or blisters. Pemphigoid, primarily affecting the elderly, results in large, itchy blisters. Pemphigus, typically striking in middle age, causes blisters inside the mouth and on the skin surface, which rupture easily and leave painful areas.
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Medications: Reactions to medications are variable. Some individuals experience increased sun sensitivity, leading to blistering sunburns. Severe reactions like TEN can involve extensive tissue damage, including the respiratory and gastrointestinal tracts, accompanied by fever and malaise.
Diagnosing Blisters
If the cause of blisters is unclear, a doctor will inquire about family history, personal medical history (including allergies and medications), and recent exposure to the sun, irritants, or allergens.
Often, the doctor can diagnose the cause based on the appearance of the blisters and the patient’s history. Suspected allergic reactions may warrant patch tests to identify the allergen. Certain blistering diseases require a skin biopsy, where a small tissue sample is examined in a laboratory.
Expected Duration of Blisters
The duration of blisters depends on the underlying cause. Irritation-induced blisters typically resolve within a few days, while those caused by infections or skin diseases may persist for weeks or months. Autoimmune blistering disorders can be chronic and require ongoing treatment. Skin infections, such as herpes simplex, may recur periodically. Inherited blistering skin diseases are also typically long-lasting.
Preventing Blisters
Several strategies can prevent blisters caused by skin irritation: wearing comfortable, well-fitting shoes with cushioned, sweat-absorbing socks; applying sunscreen; and avoiding sun exposure while taking photosensitizing medications. During cold weather, wear mittens, hats, and heavy socks to protect the skin from freezing temperatures.
Avoid irritants and allergens that trigger eczema, such as certain hygiene products, metals in jewelry (especially nickel), and irritating plants like poison ivy.
To prevent infection-related blisters, wash hands frequently and avoid touching skin sores, cuts, or open areas on others. To reduce the risk of herpes simplex, avoid sexual contact (even with a condom) with individuals who have active herpes. Minimizing the number of sexual partners also reduces the risk. To prevent the spread of childhood infections, discourage children from sharing toys and utensils that have touched another child’s mouth.
Vaccination against varicella can prevent chickenpox and help prevent shingles later in life. Adults who have not had chickenpox should avoid contact with individuals who have chickenpox or shingles until all blisters have crusted over. Shingles vaccination is routinely recommended for adults aged 50 and older.
Preventing many blistering diseases, such as hereditary and autoimmune forms, is not always possible.
Treating Blisters
Generally, it is best to leave blisters intact to protect the underlying skin and minimize the risk of infection. Cover blisters with a bandage until they heal on their own, allowing the fluid to be reabsorbed naturally. If a blister ruptures, wash the area with soap and water and apply a bandage. Large or painful blisters may be drained by a doctor, followed by application of an antibacterial cream to prevent infection.
Treatment for blisters caused by eczema, infections, and other diseases varies. Eczema may be treated with corticosteroid creams or pills. Herpes simplex infections and shingles may be treated with antiviral medications. Antibiotic creams or pills may be prescribed for impetigo. Chickenpox and coxsackievirus are typically allowed to resolve on their own; itching from chickenpox can be relieved with over-the-counter anti-itch lotions like calamine. Medication-related erythema multiforme requires immediate discontinuation of the offending medication. Corticosteroids may be prescribed.
Pemphigoid and pemphigus are treated with corticosteroids and/or other immunosuppressive agents. Dermatitis herpetiformis, associated with celiac sprue (an immune reaction to gluten), may benefit from a gluten-free diet. Porphyria cutanea tarda can be treated with regular blood removal (phlebotomy) or with medications like hydroxychloroquine or chloroquine. Inherited skin disorders causing blistering may respond to measures that protect the skin from trauma.
When to Seek Professional Medical Advice
Consult a doctor for blisters of unknown cause, very painful blisters, or blisters accompanied by other symptoms like fever and malaise. Also, seek medical attention if a blister develops signs of infection, such as increasing redness, red streaks in nearby skin, oozing blood or pus, or increased pain and swelling of the surrounding skin.
Prognosis
In many cases, blisters resolve upon removal of the cause or resolution of the infection, typically within days or weeks. Herpes infections may recur in the same location weeks, months, or even years after the initial appearance. Pemphigoid and pemphigus are typically chronic and require long-term therapy.
Additional Information
- National Institute of Arthritis and Musculoskeletal and Skin Diseases: https://www.niams.nih.gov/
- Centers for Disease Control and Prevention (CDC): https://www.cdc.gov/
