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You can get a blood blister when something pinches your skin without breaking the surface, or due to friction, like wearing tight shoes or repeatedly using a hammer. They typically go away on their own.

If you notice a raised piece of skin that has blood inside, it’s a blood blister. These blisters are not much different than ones that have clear fluid inside of them. For the most part, they are harmless and will go away within a few weeks without treatment.

A blood blister looks like a friction blister. These blisters can range in size and appear as a pocket of raised skin. Friction blisters are generally filled with clear fluid. In the case of blood blisters, pressure broke blood vessels and mixed blood with the clear fluid. This combination fills the pocket.

The blood in the blister may be red or even purplish or black in color. Generally, new blood blisters appear red and over time turn a deeper shade.

It is likely that a blood blister will form on an area of your body that is under pressure. You may get blood blisters on:

  • your mouth
  • your feet
  • your hands
  • near your joints
  • bony areas of your body like your heels, toes, or the balls of the feet

You may also get a blood blister after your skin is pinched but does not break open.

In most cases, a single blood blister is nothing to worry about. Your skin rubbing something repeatedly (like a shoe) or being pinched (like in a door) is likely the cause.

There are cases, however, when you should see your doctor:

  • You notice symptoms of infection such as warmth, or red lines leading away from the blister.
  • The blister is making it difficult for you to walk or use your hands.
  • The blister seemed to appear for no reason.
  • There are multiple blisters on your skin and you don’t know why.
  • The blister keeps coming back.
  • The blister is in your mouth or on your eyelid.
  • The blister is the result of a burn (even a sunburn) or an allergic reaction.

You may get a blood blister after something pinches your skin, but does not break the surface. Getting your hand caught in a door jamb might cause the blood blister, for example. Other reasons you may have a blood blister include:

  • participating in a sport that has you on your feet for long periods of time, such as running or dancing
  • having ill-fitting shoes that rub your skin
  • having sweaty feet that cause additional friction against your foot and your shoe
  • using a tool that rubs against your skin repeatedly, such as a hammer

Blood blisters should be left alone so they can heal. Blood blisters and friction blisters usually heal after one or two weeks. They heal because new skin forms below the blister’s raised layer. Over a period of days or weeks, the liquid in the blister will dry out.

Keep the blood blister protected as it heals. You may want to wrap it in a protective layer, such as a bandage. If the blister hurts, you can apply ice wrapped in a towel to it. You may find it helpful to take acetaminophen (Tylenol) or ibuprofen (Advil) to ease the pain.

You should not try to lance the blister, which is sometimes recommended for friction blisters without blood. The raised skin protects you from bacteria entering the blister. But contact your doctor if the pressure from the blood blister is painful and it needs to be drained.

Seeing a blister filled with blood is nothing to panic about. Blood blisters are fairly common and are generally caused by injury without the skin breaking or by friction. The best treatment for a blood blister is to let it heal on its own over a few weeks.

It’s important to determine what caused the blister. If your footwear is too tight, find shoes that fit you better. If the blood blister appeared after repetitive motion with a tool, consider protective gloves. If your feet are blistered from exercise, try wearing socks designed to wick sweat from your feet. This may reduce the friction between your foot and your shoe.