What Is a Blood Blister?
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Medically reviewed by Casey Gallagher, MD
Blood blisters, also known as hemorrhagic blisters, are a type of blister that can develop when small blood vessels beneath the skin's surface tear open due to friction or injury. This causes blood to build up between the layers of skin, creating a fluid-filled blister that is red or purple. While regular blisters are typically filled with clear fluid or pus, blood blisters are filled with blood.
Blood blisters are very common. You might want to pop a blood blister, but doing so can increase your risk of infection. Fortunately, blood blisters usually go away on their own, but some treatments can help speed up the healing process.
Symptoms
Recognizing a blood blister is usually easy. The blister will appear as a red, purple, or black fluid-filled sac on the surface of your skin. Other symptoms of blood blisters may include:
Pain and tenderness, especially if the blood blister is located near nerve endings, such as the fingers or toes
Swelling and skin discoloration around the location of the blood blister
Itching or burning sensation
If a blood blister becomes extremely swollen or painful, it might have become infected. In such cases, you'll need to receive treatment from a healthcare provider to clear up the infection. If you suspect an infection or the blister doesn't go away on its own, seek medical care as soon as you can to prevent the infection from spreading to other parts of the body.
Causes
Most blood blisters occur as a result of damage to the tissue underneath your skin. These blisters can develop anywhere, but they usually occur in areas of thicker skin such as the hands or feet. Moist skin is especially prone to developing blisters.
Blisters that are smaller than one centimeter across are known as vesicles, while larger blisters are known as bullae. Blood blisters can develop as early as a few hours after skin damage and last up to two weeks.
Any trauma to the skin can rupture blood vessels and cause blood blisters to form. Skin injuries that commonly lead to blood blisters include:
Friction or pressure: Repeated friction or pressure often occurs from wearing ill-fitting shoes or tight clothing that rubs against the skin.
Pinching or squeezing: Pinching or squeezing of the skin can lead to a blood blister. Examples of pinching or squeezing include wearing a shoe that is too tight or getting a finger stuck in a door.
Burns: Thermal burns, like those from hot liquids or surfaces, can cause the skin to blister. These blisters sometimes become blood blisters.
Frostbite: Exposure to severely cold temperatures affects the skin much like a burn does.
In some cases, a blood blister can develop on the inside of your mouth. This type of blood blister is called angina bullosa hemorrhagica. These blisters often are larger than other blood blisters and tend to be more painful. They usually break open within hours or days, leaving an open sore in your mouth. Angina bullosa hemorrhagica is rare, but can occur in people over age 30.
Experts do not know what causes blood blisters in the mouth to develop, but research suggests that an injury in the mouth may play a role. Other possible causes include regular use of topical steroids or having certain underlying conditions like diabetes. If you develop a blood blister in your mouth, visit a healthcare provider right away so they can evaluate the cause.
Diagnosis
Diagnosing a blood blister usually does not require extensive medical testing. Your healthcare provider can likely identify a blister while looking at the appearance during a physical exam. During this exam, your provider will see where the blister is located on your body and its size and color to make an accurate diagnosis.
If they are uncertain about the cause of a blister, your healthcare provider may do a skin biopsy to look for an underlying medical condition that may have led to the onset of your symptoms. This involves cutting out a piece of the blister from your skin with a small scalpel (medical knife) and looking at your skin sample underneath a microscope.
Treatment
Blood blisters typically heal on their own within a few days to two weeks, depending on the severity of the injury that caused them. Your blister can feel irritating or look unsightly—but, it's important to not pop them blister as this can cause an infection. Instead, your healthcare provider may recommend the following treatments:
Protecting the blister by placing a bandage on top or using soft padding
Trying over-the-counter pain relievers to reduce any pain or itching
Using a cold compress on top of the blister to decrease discomfort or inflammation
However, if your blood blister pops on its own, your provider may recommend a topical ointment to apply directly onto your skin and cover the sore with a sterile bandage.
If your blood blister is particularly large or painful, your provider may recommend draining the fluid from the blister. This procedure involves making a small incision (cut) in the blister and allowing the fluid to drain out. Your provider will clean the area with alcohol first and then use a sterile (clean) needle to perform the procedure. Once the procedure is done, you'll need to keep the area covered with a bandage until your skin heals.
How to Prevent Blood Blisters
Because blood blisters commonly develop on your hands and feet, you can prevent most blood blisters by protecting these areas from friction. Here are some ways to reduce friction:
Use gloves when you work with tools or use sports gear
Wear comfortable shoes that fit properly and socks with significant padding
Place tape or bandages over places on the skin that are prone to rubbing
Apply petroleum jelly on your hands and feet to reduce friction
Protection is especially important in moist conditions, such as when you know you will be sweating, because moisture softens the skin and increases the risk of friction. You can use drying agents like antiperspirants or powders to help reduce moisture.
Complications
Blood blisters are generally harmless—but they can lead to certain complications, such as:
Infection: If a blood blister pops and you don't keep it clean, you may be at an increased risk of infection. Signs of infection include increased pain, redness, warmth, and pus. An infected blood blister can progress to cellulitis, a skin infection that needs to be treated with antibiotics.
Toxic shock syndrome: Blisters that were caused by the staphylococcus aureus bacteria can potentially lead to toxic shock syndrome (TSS). TSS is a dangerous condition in which toxins enter your bloodstream and organs.
Similar Conditions
Many other underlying health conditions can cause red spots on or under the skin that can look similar to the appearance of blood blisters. These conditions include:
Thrombocytopenia: A condition that occurs when you have a low blood platelet count. People with thrombocytopenia have trouble forming blood clots to stop themselves from bleeding. One of the symptoms of the condition is having blood leak from blood vessels and collect under the skin, which results in spots that look like blood blisters.
Leukocytoclastic vasculitis: An inflammation of the blood vessels that develops in the small blood vessels underneath the skin. One symptom of this condition is blistering of the skin which may look like a collection of blood blisters.
Bullous hemorrhagic dermatosis: This condition is a possible side effect of taking the injectable blood thinner heparin. Here, the tissue underneath the skin becomes damaged, leading to black spots that look like blood blisters.
A Quick Review
While blood blisters are common, they can be alarming and possibly painful when they appear. These small, blood-filled blisters that form beneath the skin's surface are typically a result of injury or trauma. They usually heal on their own with at-home care.
However, if a blister is especially large or painful, or if it appears in your mouth, call your healthcare provider. They can rule out underlying medical causes, drain the blister if necessary, and treat any existing infection.
Frequently Asked Questions
Should you pop a blood blister or leave it?
You shouldn't pop a blood blister. These blisters usually go away on their own, and popping them could lead to infection. If the blister is painful, however, you provider can drain it with a sterilized needle.
What happens if you don't drain a blood blister?
Blood blisters typically do not need draining. They usually resolve within one to two weeks on their own.
How can you tell the difference between a blood blister and melanoma?
Some forms of melanoma may appear as red, purple, or black spots under the skin, resembling a blood blister. However, melanomas are much more likely to change shape and get larger over time, and they are much less likely to go away on their own. A healthcare provider must do a biopsy to confirm melanoma.
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