Blisters are temporary pockets filled with fluid on the outer layer of the skin. They are most common on the hands and feet. Common causes include repetitive rubbing, such as walking in ill-fitting shoes or using tools without gloves, as well as burns or excessive pressure on the skin.
While blisters are often painful and unsightly, they usually heal on their own with minimal care. Preventing blisters can be as simple as wearing properly fitting shoes, moisture-wicking socks, or protective gloves to reduce friction.
There are several types of blisters, including friction, burn, and blood blisters. Read more about the different types below.
Friction Blisters
Friction blisters are primarily caused by the repetitive action of something rubbing against your skin. Friction can be caused by walking in shoes that are too tight or using objects such as shovels for long periods of time.
Burn Blisters
Burn blisters are caused by second-degree burns (burns that injure the first two layers of skin).
After a burn causes a wound, blood vessels dilate and capillaries (tiny blood vessels) experience increased leakage. This leads to ultrafiltration of plasma (the liquid part of the blood) in the wound. When this fluid collects under the surface layers of the epidermis (the outer layer of the skin), a burn blister forms.
Blood Blisters
Injury to the skin caused by excessive force can lead to blisters, which are raised blisters filled with blood.
Angina bullosa hemorrhagic (ABH) is a type of blood blister that affects older adults. ABH usually forms on the soft palate (the muscular part of the roof of the mouth) when the mouth is injured. These blisters usually burst after a few minutes or hours, but require medical attention if they persist or do not heal on their own.
Fracture Blisters
Fracture blisters are an uncommon complication of fractures (partial or complete bone breaks) in parts of the body such as the foot, ankle, wrist, and elbow. They occur where the skin is firmly attached to the bones in places with minimal subcutaneous fat (fat under the skin).
Similar to a second-degree burn, fracture blisters can appear as clear, fluid-filled blisters or as hemorrhagic (bloody) blisters. The latter are more severe and take about 16 days to heal, while the former are considered minor injuries and heal in about 12 days.
Blisters of infection
Blisters caused by infections are small fluid-filled sacs that develop on the skin in response to certain pathogens. They are your body’s way of protecting the underlying tissue from further damage from pathogens.
Depending on the underlying cause, infection blisters can vary in size, be painful or itchy, and can be contagious.
Allergic blisters
Allergy blisters are fluid-filled bumps that can form on the skin as part of the immune response to an allergen. Some allergens, such as poison ivy, often cause blisters in most people who come into contact with them. It is also possible to get allergic blisters from contact with allergens in food, dyes, fats, fragrances and more.
Mild allergic blisters often heal on their own if you avoid the allergen. Severe or persistent reactions may require medical treatment to reduce inflammation and prevent complications.
Blister symptoms vary depending on the type, although there are some general symptoms to look out for. These include visible blister-like pockets on the skin filled with fluid or blood that appear red, dark purple, or black. Blisters can be small or large, and they can be painful.
Depending on the type, blisters can be caused by excessive force or injury to the skin, heat, moisture, friction, fractures, and certain medical conditions. Read more about the causes of different types of blisters below.
Causes of friction blisters
Friction blisters on the feet are caused by three elements: bone movement, high frictional force, and repetitive shear stress, which is when a force causes an object to deform by creating a slide along a flat surface that is parallel to the force. This blister usually affects people who hike, run, or train for the military.
Heat and humidity also contribute to friction blisters. Research shows that friction blisters are more likely to occur in warmer climates. One study found that skin temperature increases before blistering and that there is a prolonged increase in skin temperature after blistering.
Moisture from sweat or perspiration increases the force of friction, contributing to the formation of friction blisters. Research also shows that higher temperatures are associated with increased sweating, and higher walking speeds increase the temperature inside the shoe, which causes sweating – a contributing factor to blisters.
Causes of burn blisters
Burn blisters are caused by superficial second-degree burns that cause a wound in the skin.
After a burn, blood vessels dilate and capillaries experience increased leakage, leading to fluid accumulation under the epidermal layer of the skin. This causes this layer of the epidermis to separate from the dermis (the middle layer of the skin) and form burn blisters.
Causes of blood blisters
Possible causes of blood blisters include injury to the skin and repetitive activities such as lifting heavy weights.
Potential causes of ABH blisters include long-term use of inhaled corticosteroids (anti-inflammatory drugs). This can disrupt collagen formation and cause epithelial tissue (the tissue that acts as a protective covering for all body surfaces) to wear away. Further study on the causes of ABH is needed.
Causes of blister fractures
Partial or complete fractures can lead to blister fractures, which can appear as clear fluid-filled sacs or blood-filled blisters. Blisters are more likely to form where the skin attaches more tightly to the bone in areas of the body with minimal subcutaneous fat, such as the elbow, foot, or wrist.
Other causes of blisters include autoimmune health conditions such as bullous pemphigoid (when the immune system attacks the skin and causes blisters) and dermatitis herpetiformis (extremely itchy, red blisters in people with celiac disease). Autoimmune disorders occur when the body mistakenly attacks its own tissues, including the skin.
Causes of blister infection
Many types of skin infections can lead to blisters.
Herpes simplex virus (HSV)—commonly called oral herpes or genital herpes—can cause clusters of painful, clear blisters around the mouth or genitals. This is usually preceded by a tingling or burning sensation in the affected area. Over time, the blisters may burst, ooze, and cover up as part of the healing process.
Infections such as impetigo, caused by bacteria such as Staphylococcus aureus or Streptococcus pyogenesit can also lead to blisters filled with yellowish fluid.
Causes of allergic blisters
Contact dermatitis, a common allergic reaction, occurs when the skin comes into contact with substances such as poison ivy, nickel, or certain cosmetics. This reaction can lead to itchy, red skin and blisters that may ooze or appear over them.
In some cases, food allergies or medications such as antibiotics can cause a widespread reaction called urticaria or hives, which can include small blister-like lesions.
Risk factors
Risk factors for blisters include athletic activities that produce heat, moisture, and friction, such as running or hiking. Certain medical conditions and autoimmune disorders, such as bullous pemphigoid, can also increase the risk.
A healthcare professional or dermatologist can diagnose your blisters. During your exam, they’ll ask about your symptoms and examine the blisters.
They may also perform a biopsy (a sample of cells, tissue, or fluid) or order serological tests to make an accurate diagnosis. Serological tests are blood tests that detect the response and presence of antibodies, which are proteins that identify antigens or foreign substances.
Generally, blisters heal on their own. You can put a bandage on the blister to keep it clean and prevent more rubbing or friction at the blister site. It is important to manage blisters properly to help them heal and to reduce pain. It is also important to treat blisters to prevent complications or infections. Dermatologists also recommend the following tips for treating blisters:
- Use a blister pad in pressure areas, such as the bottom of your feet. There are padded bandages made specifically for blisters, or you can make a hole in the center of a medical foam pad and place it around the blister before covering it with a bandage.
- Once the blisters have drained naturally, wash the area with soap and water. Then apply Vaseline and bandage.
- Do not pop the blister. The blister roof protects the skin and promotes healing underneath.
While most blisters resolve with home care, persistent, worsening, or recurring blisters should be evaluated by a healthcare professional to determine the underlying cause and appropriate treatment.
While you can’t always avoid blisters, these tips can help prevent them:
- Wear protective gloves or equipment when using hand tools or playing sports
- Wear shoes of the correct size
- Wear well-fitting socks and opt for acrylic or nylon socks (materials that retain moisture)
- Use an over-the-counter foot powder designed to prevent blisters by providing a protective barrier effect
- Use an adhesive skin or other soft bandage if your feet or other parts of your body are more prone to chafing (chafing) or friction injuries. You can also apply powder or petroleum jelly to these areas to reduce friction.
Blisters can cause complications such as skin infections if they pop or go untreated. Improperly treated chafing blisters can lead to complications such as severe pain, cellulitis (a serious bacterial skin infection) or sepsis (a life-threatening condition where the body reacts severely to an infection).
See a doctor or visit the nearest emergency room if you experience any signs of infection (eg, pus, redness, swelling, pain) or fever. It can also become infected if the blisters and the surrounding area are warm to the touch.
You should also seek medical attention if you have several blisters or if the blisters occur alongside a medical condition such as diabetes. These conditions cause wounds to heal more slowly.
Blisters are pockets of fluid or blood on the skin that form after injury, friction, fractures, and burns. There are several types of blisters, including burn, friction, blood, and fracture blisters.
Blisters can be prevented by wearing gloves, appropriate shoes and moisture-wicking socks. Most blisters heal on their own, but you should see a doctor as soon as possible if you notice signs of infection.