A blood blister can look alarming at first glance—a dark red or purple bubble under the skin that appears suddenly and often without warning. While they’re usually harmless, blood blisters can be uncomfortable and, in some cases, signal that something more is going on. Understanding what blood blisters are and how to handle them can help you treat them safely and know when to seek medical advice.

What Is a Blood Blister?

A blood blister forms when small blood vessels (capillaries) beneath the skin rupture but the skin itself remains intact. Blood becomes trapped under the surface, creating a raised, fluid-filled pocket that appears red, maroon, or purple—darker than a typical clear blister.

Blood blisters most commonly appear on:

  • Fingers and palms

  • Toes and soles of the feet

  • Inside the mouth (cheeks, tongue, or gums)

Common Causes of Blood Blisters

Most blood blisters are caused by sudden pinching or repeated friction, such as:

  • Slamming a finger in a door

  • Wearing tight or poorly fitting shoes

  • Using tools or sports equipment without protection

  • Repetitive motions that create pressure on the skin

Blood blisters in the mouth can result from:

  • Accidental biting

  • Dental procedures

  • Sharp or poorly fitting dental appliances

In some cases, blood blisters may appear more easily in people with:

  • Thin or fragile skin

  • Circulation issues

  • Diabetes

  • Certain blood or clotting disorders

Symptoms to Expect

A blood blister may cause:

  • A raised, bubble-like area under the skin

  • Dark red, purple, or black coloring

  • Tenderness or pressure pain

  • Occasional swelling around the area

Most blood blisters are not dangerous and heal on their own within one to two weeks.

Should You Pop a Blood Blister?

In most cases, no. The intact skin over a blood blister acts as a natural barrier against infection. Popping it increases the risk of bacteria entering the wound and can slow healing.

If a blood blister bursts on its own:

  • Gently clean the area with soap and water

  • Apply an antiseptic

  • Cover with a sterile bandage

  • Keep the area clean and dry

How to Treat a Blood Blister at Home

For uncomplicated blood blisters:

  • Reduce pressure or friction on the area

  • Apply a cold compress for 10–15 minutes to reduce swelling

  • Keep the blister clean and protected

  • Wear properly fitting footwear or gloves if needed