A hematoma is a pocket of blood that collects inside your body when a damaged blood vessel leaks into surrounding tissue but the blood has no way to drain out. Unlike a regular bruise, which spreads thinly beneath the skin, a hematoma forms a distinct, often raised lump you can feel. Hematomas range from minor (under a fingernail after slamming it in a door) to life-threatening (inside the skull after a head injury), and how they’re treated depends almost entirely on where they form and how large they get.
How a Hematoma Differs From a Bruise
People often use “bruise” and “hematoma” interchangeably, but they’re structurally different. A bruise is a flat discoloration of the skin, typically greater than 1 cm across, caused by blood seeping into the upper layers of skin and the tissue just beneath it. It doesn’t create a noticeable lump. A hematoma, by contrast, produces a raised, sometimes fluctuant mass under the skin because enough blood has pooled in one spot to physically push the tissue outward. You can often feel a hematoma as a firm or spongy knot, while a bruise is flat to the touch.
Both result from damaged blood vessels, and both change color as the body breaks down trapped blood. But a hematoma involves a larger volume of blood in a more confined space, which is why it takes longer to heal and carries a higher risk of complications.
Common Types by Location
Hematomas are classified by where they form, and location is what determines how serious they are.
- Subcutaneous hematoma: The most common type, sitting just under the skin. These form after bumps, falls, or minor injuries and usually resolve on their own.
- Intramuscular hematoma: Blood collects inside a muscle, often from a sports injury or direct blow. These can be painful and limit movement, especially near joints.
- Subungual hematoma: Blood trapped beneath a fingernail or toenail, usually from a crush injury. The pressure buildup can cause intense throbbing pain.
- Epidural hematoma: Blood pools between the skull and the outer membrane covering the brain. This is a neurosurgical emergency, most often caused by a skull fracture that tears an artery.
- Subdural hematoma: Blood collects between the brain’s outer membrane and the brain itself. This can develop slowly, sometimes appearing weeks after a head injury, particularly in older adults.
- Rectus sheath hematoma: Blood collects in the abdominal wall muscles, sometimes after coughing, straining, or as a complication of blood-thinning medications.
Causes and Risk Factors
Trauma is the most straightforward cause. A fall, car accident, sports collision, or even a hard bump against furniture can rupture small blood vessels and start blood pooling. Blunt injuries account for the vast majority of trauma-related hematomas, roughly 86% in hospital settings.
Blood-thinning medications significantly increase the risk. People taking anticoagulants for conditions like atrial fibrillation or blood clots are more prone to hematomas because their blood doesn’t clot as efficiently. In one multicenter study of trauma patients who were started on anticoagulant therapy, 12.7% developed bleeding complications. Patients with more severe injuries were about three times more likely to develop these complications compared to those with milder injuries.
Other risk factors include older age (blood vessels become more fragile), liver disease (which impairs the production of clotting proteins), and low platelet counts from conditions like leukemia or certain medications. Even vigorous exercise or heavy lifting can occasionally cause a hematoma in the abdominal wall muscles if the strain is severe enough.
What a Hematoma Feels and Looks Like
A superficial hematoma typically appears as a swollen, discolored lump that feels firm or rubbery. The skin over it may be tender and warm to the touch. Over the following days, the color shifts from dark red or purple to greenish-yellow as your body gradually breaks down the trapped blood cells, just like a bruise but on a slower timeline.
Deeper hematomas inside muscles or organs may not be visible at all. Instead, you might notice pain, stiffness, or a sense of pressure in the affected area. An intramuscular hematoma in your thigh, for example, might make it painful to walk or bend your leg without any obvious surface discoloration.
Intracranial hematomas are a different category entirely. Symptoms can appear immediately after a head injury or take weeks to develop, which makes them especially dangerous. Warning signs include a headache that progressively worsens, vomiting, confusion, slurred speech, drowsiness that deepens over time, dizziness, pupils that are noticeably different sizes, seizures, and loss of consciousness. Someone who seems fine after a head injury but later becomes confused or loses consciousness needs emergency care immediately.
How Hematomas Are Diagnosed
Most superficial hematomas are diagnosed with a physical exam alone. Your doctor can feel the lump, note the discoloration, and assess whether it needs any treatment beyond basic care.
Internal hematomas require imaging. CT scans are the first-line tool, especially for head injuries, because they’re fast and widely available. A CT will show a hematoma as a well-defined, often circular or oval mass with clear borders. For hematomas inside the brain, MRI provides more detailed information. MRI can distinguish a hematoma from a tumor or abscess by identifying a characteristic ring of iron deposits left behind by broken-down blood cells, something CT often misses. In practice, emergency departments almost always start with a CT and follow up with MRI when more detail is needed.
Treatment: When to Wait and When to Act
Small, superficial hematomas need nothing more than rest, ice, compression, and elevation. Applying ice in 20-minute intervals during the first 48 hours helps limit swelling. Most of these resolve on their own as the body gradually reabsorbs the pooled blood.
Larger or more painful hematomas sometimes need to be drained. A doctor can use a needle to aspirate the collected blood, or make a small incision if the hematoma has started to clot and solidify. Subungual hematomas, the kind under a fingernail, are often relieved by making a tiny hole in the nail to release the trapped blood and relieve pressure.
Intracranial hematomas follow much stricter guidelines. For epidural hematomas (between the skull and the brain’s outer membrane), surgical evacuation is recommended when the blood collection exceeds 30 cubic centimeters, regardless of how alert the patient is. Smaller ones can sometimes be monitored with repeated CT scans and close neurological observation, but only in a facility equipped for neurosurgery. Hematomas located near the temples are more likely to worsen and lower the threshold for surgery. For hematomas deeper in the brain, a volume of roughly 12 to 15 cubic centimeters is the decision point: above that range, surgery is associated with better survival, while below it, conservative management tends to produce better functional outcomes.
Healing Timeline
A small subcutaneous hematoma typically resolves in one to four weeks, following the same color-change progression as a bruise but more slowly. The lump gradually softens and flattens as your body’s immune cells clear away the old blood.
Deeper or larger hematomas take considerably longer. A rectus sheath hematoma in the abdominal wall, for instance, typically takes two to three months to be fully reabsorbed. Intramuscular hematomas in the legs or arms can take a similar amount of time, especially if the affected muscle is large or if you’re on blood thinners that slow the clotting process.
During healing, you may notice the area remains slightly firm or tender even after the discoloration fades. This is normal. The tissue underneath is still being remodeled.
Potential Complications
Most hematomas heal without lasting problems, but a few complications are worth knowing about.
Infection is one risk, particularly if the hematoma is large. A pool of stagnant blood creates a warm, nutrient-rich environment that bacteria can colonize. Signs of infection include increasing redness, warmth, fever, and worsening pain days after the initial injury.
A condition called myositis ossificans can develop when bone tissue forms inside a muscle at the site of a previous hematoma. This usually happens after a significant muscle injury, particularly in the thigh or upper arm. You might notice a hard lump that develops weeks after the original injury, along with reduced range of motion if the growth sits near a joint. Stiffness from myositis ossificans can linger for several months, though most cases eventually improve with physical therapy.
Compartment syndrome is a rarer but more urgent complication. If a hematoma forms inside a tight muscle compartment, typically in the lower leg or forearm, the pressure can cut off blood flow to the surrounding tissue. Severe, disproportionate pain, numbness, and a feeling of tightness in the affected limb are the hallmark signs and require immediate surgical intervention to relieve the pressure.