A blood blister can look alarming at first—a dark red or purple bubble trapped beneath the skin—but most cases are harmless. These blisters form when small blood vessels break while the outer skin remains intact, allowing blood to pool underneath. Blood blisters are commonly found on fingers, palms, toes, soles of the feet, or inside the mouth, and while uncomfortable, they usually heal on their own within one to two weeks.

The most common causes include sudden pinching, repeated friction, or pressure from tight shoes, tools, or sports equipment. Oral blood blisters may occur after accidental biting or dental work. Some people develop them more easily due to thin skin, circulation problems, diabetes, or blood-clotting disorders. Typical symptoms include a raised bubble, dark coloring, tenderness, and mild swelling around the area.

Popping a blood blister is not recommended, as the skin protects against infection. Instead, reduce pressure, keep the area clean, and apply a cold compress to ease swelling. If a blister bursts naturally, clean it gently and cover it. Seek medical advice if blisters recur frequently, show signs of infection, or take longer than two weeks to heal.