What Is a Blood Blister?

Blood blisters are raised sacs on the skin that contain blood. They are fairly common and occur when the skin is under pressure or pinched, but doesn't break. Blood vessels open up and the blood pools, filling the pocket in the skin.

A blood blister is similar to a friction blister you might get when your shoe rubs against your heel, but it is filled with blood instead of clear liquid. The blood will initially be red, then turn darker as days pass.

Most of the time, blood blisters disappear on their own and do not pose any significant health concerns. But there are times when an evaluation is needed to rule out an underlying condition.

Here's what you need to know about how to spot a blood blister, when and how to care for one, when to see a healthcare provider, and how to prevent a blood blister from forming.

Signs and Symptoms of a Blood Blister

Like friction blisters, blood blisters are raised pockets on the skin. They are filled with blood that may be red, purple, or black.

The deeper layers of the skin are affected and the cells above the blister die off. The encapsulated blood will darken with time.

The skin’s blood vessels sustain some mild damage, often dilating as part of an immune response to the dying cells, and inflammation occurs. You may experience:

• Pain at or around the site
• Skin redness around the blister
• Itchiness

Blood blisters can vary in size. Smaller blisters may be called vesicles, while larger ones may be referred to as bulla.

Common Locations

There are a few areas where blood blisters are likely to pop up. They include:

• Hands
• Fingers
• Feet
• Mouth
• Areas of the body that are subject to excessive friction
• Places where the skin has been pinched (like a finger that got stuck in a door)
• Close to joints
• Near bony prominences
  

Causes of Blood Blisters

While blood blisters can happen to anyone, they are most common in active people (such as athletes or dancers) and individuals who wear shoes that don’t fit their feet properly.

People who have jobs and hobbies that involve manual labor are also at risk of developing blood blisters.

Some of the reasons a person may get blood blisters are as follows:

• The skin is pinched and doesn’t break open.
• The skin is exposed to a high amount of friction, such as when walking, lifting weights, or using a tool.
• Poorly fitted shoes cause excess friction on heels and bony areas of the toes like bunions.
• Feet are more prone to blistering when they are wet—moisture softens the skin and makes it more susceptible to friction.  
• Frostbite might lead to blood blisters.
• People with certain diseases, like kidney failure, may experience blood blisters in the mouth
• People taking certain medications, such as blood-thinners, may be more at risk of developing blood blisters.
  

When to Visit a Healthcare Provider

Oftentimes, the diagnosis of a blood blister is relatively straightforward. For example, you may discover the formation of a blood blister after you’ve experienced a minor trauma to the skin.

In many cases, you’ll be able to identify the blood blister yourself and you won’t require medical evaluation or intervention. Just leave the blister alone and give it time to heal.

However, if any of the following apply, a trip to the healthcare provider is in order to rule out other possible conditions and ensure proper healing:

• The blood blister(s) has emerged for no known reason.
  
• The pain caused by the blood blister is impeding your ability to do your daily activities.
• The blister shows signs of an infection like redness, swelling, and the feeling of being hot to the touch.
• The blood blister goes away, then comes back again.
• You find the blister in an unexpected place, such as your mouth, eyelids, or genital region.
• You have/could have an underlying illness that may make healing more difficult for your body (e.g., diabetes)
  
• The blister appears following an allergic reaction, burn, or sunburn.
• A lump is fast-growing, especially if it itches, stings, oozes, or bleeds. This can be a sign of nodular melanoma, an aggressive form of skin cancer that can look like a blood blister.

Diagnosis

If you see a healthcare provider for a blood blister, they will likely be able to diagnose it just by asking you about any recent traumas to the area and performing a physical exam.

They will also look for signs of infection, so that they can treat you appropriately if needed.

If they cannot confidently diagnose you with a blood blister, or if it's in an odd location, they may take a sample of the blood in the blister (biopsy) to be examined in a lab.

Blood Blister vs. Nodular Melanoma

Nodular melanoma, a type of skin cancer, is one possible alternative diagnosis that your healthcare provider may consider. This blood blister lookalike grows rapidly—typically over the course of several weeks or months—so it's important to catch it as early as possible.

If suspected, a biopsy is critical. There is no easy way to tell the difference between a blood blister and a malignant (cancerous) lump with a physical exam alone, given their similarities.

Unlike other forms of skin cancer, nodular melanomas are typically symmetrical like a blister. They may also be smooth like a blood blister, though they can also be rougher and crusty.

While nodular melanomas are often black or dark in color, about one-third of nodular melanomas are flesh-toned. A nodular melanoma may or may not be ulcerated (broken open). The lump may also be very itchy.

Blood Blister Treatment

Most of the time, the blister will heal on its own as long as you remove the trauma or repetitive movement that initially caused it.

If your blister causes discomfort, over-the-counter pain relievers like ibuprofen or acetaminophen may be sufficient to ease the pain.

You may also want to wrap a blood blister on your finger or toe with gauze and/or a bandage to protect it for rupturing. If it does rupture, it's important to clean it with soap and water, and wrap it with a protective layer to prevent infection.

To ease pain and swelling from a blister in your mouth, you can place a little crushed ice on the sore for a few minutes at a time, several times per day.

Should You Pop or Drain a Blood Blister?

Although you may be tempted to pop the blood blister, experts recommend resisting the urge to do so. The layer of skin that covers the blister helps protect it from infection. Over time—about one to two weeks—the blood blister should dry up on its own.

That said, large and painful blisters may need to be drained to relieve discomfort or pain. This can be done by sterilizing a small needle with rubbing alcohol and gently piercing one edge of the blister to drain fluid.

When fluid has been drained, wash the area with soap and water. Afterward, apply petroleum jelly and cover the blister.

Prevention

Some blood blisters, like those due to unavoidable accidents, may be impossible to prevent. But there are few things you can do to decrease the likelihood of developing a blood blister from other means.

Follow these tips:

• Wear gloves if you plan to work with your hands or use tools or other equipment that requires repetitive motion and would cause friction on your skin.
• Make sure that your shoes fit you properly and that they aren’t causing pressure points on your skin.
• Wear socks with your shoes.
• If you notice that some areas of pressure are forming, you may need to protect your skin with adhesive padding or moleskin until you have broken in your shoes.
• If your feet get sweaty, you may find that placing some powder in your shoes helps to soak up extra moisture.
• Use lubricants on your feet to reduce friction on your skin.
• If your shoes continue to cause painful blood blisters, you may need to consider investing in a new pair.

A Word From Verywell

Generally, you can prevent blood blisters from forming if you use properly fitted hand and footwear. If you happen to acquire a blood blister, they’ll typically heal without causing you a lot of trouble.

However, if blood blisters show up in unusual places and you can’t pinpoint a reason, it’s a good idea to make an appointment with your healthcare provider to rule out other medical conditions.