Blood blisters can look alarming when they suddenly appear on the skin. They usually show up as dark red, maroon, or purplish bubbles beneath the surface and may cause mild discomfort or tenderness. Despite their dramatic appearance, most blood blisters are harmless and heal on their own within a short time. They form when tiny blood vessels under the skin break while the top layer of skin remains intact. The leaked blood becomes trapped underneath, creating a raised blister filled with dark fluid. Blood blisters most often appear on the fingers, palms, toes, and soles of the feet, but they can also develop inside the mouth on the cheeks, tongue, or gums.The most common cause of a blood blister is sudden pressure or repeated friction against the skin. This can happen when a finger gets caught in a door, when tight or poorly fitting shoes rub against the feet, or when tools and sports equipment are used without proper protection. Activities that involve repetitive motions can also lead to blisters by constantly pressing on the same area of skin. Inside the mouth, blood blisters may form after accidentally biting the cheek or tongue, during dental procedures, or from irritation caused by sharp or poorly fitting dental appliances.

A typical blood blister appears as a raised, bubble-like spot beneath the skin. It may look dark red, purple, or even black depending on how much blood collects under the surface. The area might feel tender, slightly swollen, or painful when pressure is applied. In most cases, the blister will gradually dry out and heal within one to two weeks without medical treatment.It is usually best not to pop a blood blister. The skin covering it acts as a natural barrier that protects the wound from infection. If the blister bursts on its own, the area should be gently cleaned with soap and water, treated with an antiseptic, and covered with a clean bandage to keep it protected while it heals.