A blood blister can be startling at first sight—a dark red or purplish bubble beneath the skin that seems to appear out of nowhere. Although they’re generally harmless, blood blisters can be uncomfortable and may sometimes indicate an underlying issue. Knowing what blood blisters are and how to care for them can help you manage them properly and recognize when medical attention might be needed.
What Is a Blood Blister?
A blood blister develops when tiny blood vessels (capillaries) under the skin break while the outer layer of skin stays intact. The leaked blood becomes trapped beneath the surface, forming a raised, fluid-filled spot that looks red, maroon, or purple—noticeably 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 the results of 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.
