My daughter just woke up with a large spot on her foot, and I have no idea what it is. She’s in pain and can’t move her foot. What could be causing this? Please explain.

A blood blister can be startling when it first appears. One moment, your skin looks normal, and the next there’s a dark red or purple bubble just beneath the surface. It can appear serious, even alarming, especially if it shows up suddenly or on a sensitive area. Most of the time, though, blood blisters are harmless. They usually result from minor injury, pressure, or friction. Still, they can be uncomfortable, sometimes painful, and occasionally indicate a deeper concern. Knowing what blood blisters are, how they form, and how to care for them can help you stay calm, treat them properly, and recognize when medical advice may be needed.

At its core, a blood blister forms when tiny blood vessels under the skin are damaged but the skin above remains unbroken. These vessels, called capillaries, are delicate. When pinched, squeezed, or rubbed repeatedly, they can rupture. Instead of bleeding outward, the blood collects beneath the skin, trapped under the intact outer layer. This pooled blood creates a raised pocket of dark fluid, giving the blister its deep red, maroon, or purple color—darker than the clear or pale fluid found in a standard blister.

Blood blisters can appear in many areas, though they most often develop where skin experiences friction or pressure. Fingers and palms are common, especially for people who use their hands heavily or handle tools regularly. Toes and the soles of the feet are frequent sites as well, often due to tight shoes or extended walking or standing. Blood blisters may also appear inside the mouth—on the cheeks, tongue, or gums—where they can be particularly uncomfortable because of constant movement and sensitivity.

The usual causes of blood blisters are everyday accidents and repeated stress on the skin. Slamming a finger in a door, dropping a heavy object on a toe, or gripping something too tightly can all damage the small vessels beneath the skin. Shoes that are too tight, loose, or poorly designed can create constant rubbing, especially during exercise or walking. Tools and sports equipment can also contribute, particularly when used long periods without padding or gloves. Even repetitive motions that seem harmless can eventually put enough pressure on the skin to cause a blood blister.

Inside the mouth, blood blisters often have different triggers. Accidentally biting the cheek or tongue is common. Dental procedures can sometimes irritate soft tissues, leading to small injuries that form blood blisters. Sharp teeth, braces, dentures, or other appliances can rub against delicate tissues, causing trauma. Oral blood blisters usually heal quickly, but they can still be painful while present.

Some people develop blood blisters more easily than others. Fragile or thin skin is one factor, and aging or sun damage can reduce skin protection over vessels. Circulation problems may weaken vessels or slow healing. Conditions like diabetes affect both circulation and skin health, making injuries more likely and recovery slower. Blood or clotting disorders can also increase the likelihood of blood collecting under the skin from minor pressure, leading to more frequent blisters.

Blood blisters are usually easy to identify. They appear as raised, bubble-like areas under the skin filled with dark fluid. Colors range from deep red to purple or black depending on the blood volume and blister age. The area may feel tender, with pressure or throbbing, especially if the blister is large or in a frequently used location. Mild swelling can occur, though severe swelling is uncommon unless infection or a more serious injury is present.

Most blood blisters are not dangerous. The body usually resolves them on its own as the trapped blood is reabsorbed, and the blister flattens and fades. Healing generally takes one to two weeks, though larger blisters or those in high-friction areas may take longer. If the skin remains intact and there are no infection signs, simple care is sufficient.

A common question is whether to pop a blood blister. Typically, the answer is no. The skin covering the blister acts as a protective barrier, keeping bacteria and dirt out. Breaking the blister creates an open wound, which can become infected and take longer to heal. Despite the temptation, especially if the blister feels tight or painful, leaving it alone is usually best.

Sometimes a blood blister may burst naturally due to rubbing or thinning of the skin. If this happens, proper care is essential. Clean the area gently with mild soap and water, apply an antiseptic to reduce infection risk, and cover it with a sterile bandage. Keep the wound clean and dry, changing the bandage regularly until healed.

Home care for blood blisters focuses on comfort and preventing further injury. Relieve pressure or friction that caused the blister, such as switching shoes, wearing gloves, or padding tools. Applying a cold compress for ten to fifteen minutes can reduce swelling and ease pain soon after formation. Keep the skin clean and cover the blister loosely if it might be rubbed or bumped. Avoid harsh chemicals or unverified home remedies, as these can irritate the skin or raise infection risk. Healing may involve color changes and slight peeling, which is normal.

Oral blood blisters need particular care because the mouth is warm and moist, encouraging bacterial growth, though it also heals faster than other areas. Mouth blisters often resolve within days. Rinsing with warm salt water can clean the area, reduce irritation, and soothe discomfort. Avoid hot, spicy, acidic, or sharp foods that could aggravate the blister. Soft, cool foods are usually more comfortable during healing.

Frequent or unexplained oral blood blisters could indicate underlying problems. Recurrent blisters may stem from dental issues like poorly fitting appliances or sharp teeth, but they could also signal broader health concerns. Consulting a dentist or doctor can identify causes and help prevent recurrence.

While most blood blisters heal on their own, medical advice is warranted in some cases. Seek evaluation if a blister is extremely painful, enlarging, or slow to heal. Signs of infection—such as increased redness, warmth, swelling, pus, or fever—also require attention. Recurrent blisters without obvious cause, especially in people with diabetes, circulation issues, or bleeding disorders, should be investigated. If a blister lasts more than two weeks, consulting a healthcare professional is recommended.

Rarely, persistent or unexplained blood blisters may indicate underlying medical conditions needing attention. Though uncommon, this highlights the importance of noticing patterns in frequency and location for medical guidance.

Prevention is crucial, particularly for those prone to blood blisters. Properly fitting shoes reduce foot friction, and protective gloves shield hands during manual work or sports. Adding padding to tools or equipment can help. Moisturizing skin maintains flexibility and strength, lowering injury risk. Managing underlying health conditions also supports skin resilience and healing.

Small lifestyle changes can make a significant difference. Taking breaks from repetitive tasks, adjusting grip on objects, and noticing early irritation can prevent painful blisters. Regular dental care and properly fitting appliances reduce oral injury risks.

Blood blisters are mostly minor injuries caused by pressure or friction. They often look worse than they are and usually heal without special treatment. While uncomfortable, they are generally harmless and short-lived. Understanding their causes and proper care makes them easier to manage and less stressful.

Paying attention to your body is always important. Rare blisters with clear causes usually need only home care. Frequent, unexplained, or slow-healing blisters should prompt professional evaluation. The body often gives small signals for larger issues, and early attention can make a meaningful difference.