A hematoma is a collection of blood that pools outside of a blood vessel, forming a distinct pocket or mass inside your body. Unlike a simple bruise, which is a thin layer of leaked blood visible through your skin, a hematoma involves enough trapped blood to fill a space and push against surrounding tissues. Hematomas range from minor and painless to life-threatening, depending on where they form and how large they grow.
How a Hematoma Differs From a Bruise
Bruises and hematomas both involve blood leaking from damaged vessels, but they’re not the same thing. A bruise is a flat discoloration where a small amount of blood spreads thinly beneath the skin. A hematoma, by contrast, collects in a defined pocket. That pooled blood can’t flow or drain away on its own, so it builds up and creates a lump you can often feel. When a doctor presses on a hematoma, it feels distinctly different from the healthy tissue around it: firmer, sometimes rubbery, and often tender.
Shallow hematomas near the skin surface produce visible color changes similar to bruises but with noticeable swelling underneath. Deeper hematomas, buried inside muscles or organs, may not show any surface discoloration at all. Their main signs are pain, swelling, and a sense of pressure in the area.
Types of Hematomas by Location
Hematomas are classified by where in the body they form, and location largely determines how serious they are.
- Subcutaneous hematomas sit just under the skin. These are the most common type and usually result from bumps, falls, or minor injuries. They look like large, raised bruises.
- Intramuscular hematomas form within muscle tissue, often from sports injuries or significant impacts. They cause deep aching, stiffness, and reduced range of motion in the affected area.
- Subungual hematomas develop under a fingernail or toenail, typically after something crushes or strikes the nail. The trapped blood creates intense throbbing pressure because the nail prevents the area from swelling outward.
- Intracranial hematomas form inside or around the brain. These include subdural hematomas (between the brain and its outer covering) and epidural hematomas (between the skull and that covering). Both are medical emergencies.
Common Causes and Risk Factors
Most hematomas result from trauma: a fall, a car accident, a surgical procedure, or even a hard bump against furniture. The force damages a blood vessel, and blood leaks into the surrounding tissue faster than the body can contain it.
But some hematomas form without any obvious injury. These spontaneous hematomas are strongly linked to blood-thinning medications. In one study of patients hospitalized for spontaneous soft-tissue hematomas, 79% were taking anticoagulant therapy, and another 13% were on a combination of anticoagulant and antiplatelet drugs. Only a small fraction had no medication involvement at all, and most of those patients had underlying bleeding disorders like hemophilia or abnormally low platelet counts.
Other factors that raise your risk include aging (blood vessels become more fragile), liver disease (which impairs the body’s ability to form clots), and heavy alcohol use. Even vigorous exercise can occasionally cause intramuscular hematomas in people who are otherwise healthy.
Symptoms to Recognize
What a hematoma feels like depends on its size and depth. Near the skin surface, you’ll typically notice swelling, tenderness, warmth, and skin that looks reddish-purple before gradually shifting through shades of blue, green, and yellow as the blood breaks down. The area may feel firm or boggy to the touch.
Deeper hematomas are harder to detect visually. A hematoma inside a muscle might feel like a persistent cramp or tightness that doesn’t ease with stretching. You might notice reduced strength or flexibility in that limb. Large internal hematomas can cause a drop in blood pressure if enough blood accumulates outside the vessels, leading to lightheadedness or fatigue.
When a Hematoma Is an Emergency
Intracranial hematomas are the most dangerous type because the skull leaves no room for expansion. As blood pools, it compresses brain tissue. Symptoms can appear immediately after a head injury or develop gradually over days to weeks, which makes them particularly deceptive. Warning signs include a headache that won’t go away, increasing drowsiness, confusion, slurred speech, vomiting, blurred vision, unsteadiness, pupils that appear different sizes, and loss of consciousness. Someone who seems fine after a head injury but later becomes confused or passes out needs immediate emergency care.
Outside the head, a hematoma becomes urgent when it’s rapidly expanding, causing severe pain, or compressing nerves or blood vessels. Signs of nerve compression include numbness, tingling, or weakness below the site of the hematoma.
How Hematomas Are Diagnosed
Superficial hematomas are usually diagnosed by physical exam alone. A doctor can see the discoloration and feel the pooled blood beneath the skin. For deeper or more serious hematomas, imaging is essential. CT scans are the most commonly used tool, especially for suspected bleeding inside the skull, because they’re fast and clearly show where blood has collected. MRI scans provide more detail for soft-tissue hematomas in muscles or organs. Ultrasound is sometimes used for hematomas near the surface or in the abdomen.
For intracranial hematomas, repeat imaging is often necessary because bleeding can worsen over time. Patients may undergo several CT scans over days or weeks to track whether the blood collection is growing, stable, or shrinking.
Treatment Options
Small, superficial hematomas generally resolve on their own. The body gradually reabsorbs the trapped blood over one to four weeks, depending on the size. You can speed this process and manage discomfort using a few straightforward steps:
- Rest the injured area to prevent further damage and give your body’s healing systems time to work.
- Ice applied in 10-minute intervals helps reduce pain and slow additional bleeding into the tissue.
- Compression with an elastic bandage applies gentle pressure to limit swelling. Wrap snugly but not so tight that you feel numbness or tingling.
- Elevation above heart level slows blood flow to the area, reducing both bleeding and swelling.
Hematomas that are larger, painful, or located in sensitive areas may need medical drainage. For subungual hematomas (under the nail), a procedure called trephination relieves the pressure by creating a small hole in the nail to let the blood escape. This is typically done within 48 hours of the injury and provides near-immediate pain relief. Nail removal was once standard for hematomas covering more than half the nail surface, but current practice favors the simpler drainage approach for uncomplicated cases. Full nail removal and surgical repair are reserved for situations involving a significant tear in the nail bed, a displaced fracture of the fingertip bone, or damage extending into the nail’s growth center.
Intracranial hematomas often require surgical evacuation, where a surgeon opens a section of the skull to remove the collected blood and relieve pressure on the brain. The urgency depends on the size of the hematoma and how quickly symptoms are progressing.
Healing Timeline and Potential Complications
Most soft-tissue hematomas follow a predictable healing arc. In the first few days, the pooled blood is dense and dark. Over the next one to two weeks, the body’s cleanup cells break down the blood, and the area gradually softens and changes color. Small hematomas may fully resolve in one to two weeks. Larger ones can take four to six weeks, and very large collections occasionally leave behind a firm, calcified lump as the body walls off blood it can’t fully reabsorb.
Infection is the most serious complication of a significant hematoma. Pooled blood creates a warm, nutrient-rich environment where bacteria can thrive. Research on hematomas forming after implanted cardiac devices found that clinically significant hematomas carried a more than sevenfold increased risk of infection compared to patients without hematomas. That infection risk persisted for a full year. While this data comes from a surgical context, the principle applies broadly: any large, unresolved hematoma is a potential site for bacterial growth.
In muscles, a hematoma that doesn’t heal properly can trigger a process where the body deposits bone-like calcium deposits in the soft tissue, a condition called myositis ossificans. This is most common in the thigh after a significant impact and can cause lasting stiffness if not managed early with appropriate physical therapy.