A hematoma is a collection of blood that pools outside of blood vessels, usually after an injury ruptures a vein or artery. Unlike a simple bruise, where blood seeps diffusely into soft tissue, a hematoma forms a distinct, often palpable mass that can range from a pea-sized bump under a fingernail to a life-threatening bleed filling the space behind the abdominal organs. How a hematoma behaves, how long it lasts, and whether it needs medical attention depends almost entirely on where in the body it forms and how much blood has accumulated.
How a Hematoma Forms
When a blood vessel breaks, blood escapes into the surrounding tissue. In most minor injuries, the body’s clotting system seals the leak quickly, and the small amount of escaped blood spreads thinly through the tissue as a bruise. A hematoma develops when enough blood collects in one spot to form a localized pocket. After vessel rupture, the initial hematoma can sometimes continue expanding if clotting is delayed or if the damaged vessel keeps leaking.1PubMed. The Pathophysiology of Intracerebral Hemorrhage Formation and Expansion The pooled blood clots into a semi-solid mass, and the surrounding tissue swells in response. Over the following hours and days, the body begins breaking down the trapped blood, which is why a hematoma often changes color from deep red or purple to green, yellow, and brown as the hemoglobin inside the clot is chemically dismantled.
The size of a hematoma depends on several factors: the caliber of the ruptured vessel, how quickly the clotting cascade kicks in, and whether the surrounding tissue is tight enough to compress the leak. A small capillary bleed in the skin might produce a lump the size of a marble. A torn artery deep in the pelvis can dump enough blood to cause shock.
Common Types and Where They Happen
Hematomas are generally named for their location, and location is what separates a nuisance from an emergency.
- Subcutaneous hematomas: These sit just under the skin, often from a bump or fall. They’re the most familiar type, appearing as a raised, tender, discolored lump. Most resolve on their own over a few weeks.
- Subungual hematomas: Blood trapped under a fingernail or toenail after a crush injury. The pressure buildup causes intense, throbbing pain and a dark blue-black discoloration under the nail. Draining the blood through a small hole in the nail provides immediate relief.2The Journal of Emergency Medicine. Use of an 18-Gauge Needle to Evacuate Subungual Hematomas
- Intramuscular hematomas: Blood pooling within a muscle belly, common after sports injuries or direct blows. These can cause significant stiffness and pain, and occasionally lead to complications if the muscle compartment is tight.
- Intracranial hematomas: Blood collecting inside the skull, either between the brain and its protective membranes (epidural or subdural) or within the brain tissue itself. These are the most dangerous variety because the rigid skull leaves no room for expansion, and even a modest blood collection can compress brain tissue.
- Retroperitoneal hematomas: Blood accumulating in the space behind the abdominal organs, often from pelvic fractures or aortic injuries. The retroperitoneal space can hold a very large volume of blood before symptoms become obvious, making these bleeds particularly treacherous.3PubMed Central. Rehabilitation Training Following Retroperitoneal Haemorrhage: A Case Report and Review of the Literature
- Rectus sheath hematomas: Bleeding within the abdominal wall muscles, sometimes triggered by coughing, straining, or anticoagulant use. These can mimic other causes of abdominal pain and occasionally lead to dangerous blood loss.4PubMed. Diagnosis of Rectus Sheath Hematoma by Point-of-Care Ultrasound
How the Body Clears a Hematoma
Left alone, most hematomas are gradually broken down and reabsorbed by the body. The process relies on immune cells, primarily a type of white blood cell that engulfs and digests dead red blood cells and clot debris. Researchers are actively studying how to speed this natural cleanup, particularly in the brain, where a lingering hematoma causes ongoing damage. Both surgical removal and methods that boost the body’s own phagocytic cleanup are under investigation, with the goal of limiting tissue injury from the toxic byproducts of red blood cell breakdown, especially free hemoglobin and iron.5PubMed Central. Hematoma clearance as a therapeutic target in intracerebral hemorrhage: From macro to micro
A specific receptor on immune cells, called CD36, appears to play a central role in hematoma absorption. When this receptor is absent or underperforming, the rate of hematoma clearance drops and neurological outcomes worsen.6PubMed Central. CD36-Mediated Hematoma Absorption following Intracerebral Hemorrhage: Negative Regulation by TLR4 Signaling This finding has mostly been studied in brain hemorrhages, but the general principle holds elsewhere in the body: the immune system’s ability to eat the clot determines how quickly the hematoma resolves.
For a small subcutaneous hematoma, resorption might take a week or two. A large intramuscular hematoma can linger for months. And in some cases, the body never fully clears the blood collection, leading to chronic or calcified hematomas discussed further below.
When a Hematoma Becomes Dangerous
The danger of a hematoma is almost always about pressure and location, not the blood loss itself (though massive bleeds are an exception). Inside the skull, even a relatively small volume of trapped blood can compress the brain and become life-threatening within hours. In a limb, a hematoma expanding within a tight muscle compartment bounded by bone and tough connective tissue can cut off blood flow to the muscles and nerves downstream, a condition known as compartment syndrome. This is a surgical emergency: without rapid decompression, permanent muscle death and nerve damage follow.7PubMed. Acute limb compartment syndrome: a review
In the abdomen and pelvis, the picture is different. Retroperitoneal hematomas from pelvic fractures carry a high risk of hemorrhagic shock because the space can accommodate liters of blood before the expanding mass triggers obvious external signs. Pelvic fractures with retroperitoneal bleeding are a significant cause of death in trauma patients.8Medicni perspektivi. Clinical case of a pelvic fracture with massive retroperitoneal hematoma When arterial bleeding is the source, angiographic techniques can locate and plug the leaking vessel.9PubMed. Diagnosis and treatment of retroperitoneal hematoma in multiple trauma patients
Medications That Raise Your Risk
Blood-thinning medications and antiplatelet drugs are among the most common reasons a minor bump turns into a significant hematoma. Anticoagulants like warfarin, heparin, and the newer direct oral anticoagulants slow clot formation, giving blood more time to pool before the leak seals. Antiplatelet drugs, including aspirin and clopidogrel, impair the first wave of the body’s clotting response, and several reports indicate that antiplatelet medications can increase both hematoma expansion and mortality in the context of brain hemorrhages.10PubMed Central. Hematoma Expansion following Intracerebral Hemorrhage: Mechanisms Targeting the Coagulation Cascade and Platelet Activation
If you take any blood-thinning medication and develop a new hematoma, especially one that keeps growing or causes significant pain, it’s worth getting medical advice promptly. The same applies after procedures: cardiac catheterization through the femoral artery in the groin, for example, produces hematomas in roughly one in ten patients.11PubMed. Femoral artery complications after cardiac catheterization: a study of patient profile Most of these are small and self-limiting, but in patients on anticoagulants the risk of significant expansion is higher.
Bleeding Disorders and Spontaneous Hematomas
People with inherited bleeding disorders like hemophilia or von Willebrand disease can develop hematomas with little or no apparent trauma. Deep hematomas, joint bleeds, and gastrointestinal bleeding are among the most frequent problems in these conditions.12PubMed. Rare and unusual bleeding manifestations in congenital bleeding disorders: an annotated review More unusually, hematomas within the wall of the intestine can cause partial bowel obstruction, mimicking surgical emergencies that have nothing to do with bleeding. The broader lesson is that congenital bleeding disorders can produce hematomas in virtually any tissue, and physicians treating these patients need to consider bleeding as a cause of unexplained symptoms even in unlikely locations.
Spontaneous hematomas in someone with no known bleeding disorder are worth investigating. Repeated bruising or hematoma formation without clear injury can be an early sign of a platelet problem, a clotting factor deficiency, or, less commonly, a blood cancer affecting the bone marrow.
Infection Risk
A hematoma is, at its core, a stagnant pool of nutrient-rich blood, and bacteria thrive in that environment. This risk is well documented in nasal septal hematomas, which can form after a blow to the nose. When blood collects between the cartilage and its lining membrane, it cuts off the cartilage’s blood supply. If bacteria colonize the hematoma, an abscess can form, and cartilage destruction can begin within 24 to 48 hours.13Journal of the Korean Association of Oral and Maxillofacial Surgeons. Nasal septal abscess with a dental origin: a case report and a review of the literature The combination of tissue ischemia and bacterial growth creates an ideal setup for rapid abscess formation.14PubMed Central. Recurrent Nasal Septal Hematoma and Abscess: A Rare Manifestation of Leukemia Left untreated, an infected nasal septal hematoma can destroy the structural support of the nose, leading to a visible deformity called a saddle-nose collapse.
The infection risk isn’t unique to the nose. Any hematoma near a wound, surgical site, or area of compromised tissue can become infected. Postoperative hematomas are one reason surgeons are careful about hemostasis during closure and sometimes place drains. If a hematoma becomes warm, increasingly painful, or develops overlying redness days after the initial injury, infection should be suspected.
How Hematomas Look on Imaging
Doctors use different imaging tools depending on where a hematoma is suspected. For superficial or abdominal hematomas, ultrasound is often the fastest and most accessible option. Point-of-care ultrasound in the emergency department can rapidly identify a rectus sheath hematoma or an iliopsoas hematoma (a deep bleed in the hip flexor muscle), helping doctors make time-sensitive treatment decisions.15Critical Ultrasound Journal. Diagnosis of traumatic iliopsoas hematoma using point-of-care ultrasound CT scans are the standard for evaluating intracranial and retroperitoneal hematomas because they provide fast, detailed images of deep structures.
MRI offers something neither ultrasound nor CT can match: the ability to estimate the age of a hematoma. As trapped blood ages, the hemoglobin molecules inside the red blood cells go through a predictable chemical transformation. Radiologists can identify five distinct stages of a brain hemorrhage on MRI based on whether the hemoglobin is still carrying oxygen, has lost it, has been converted to methemoglobin, or has broken down entirely into iron-storage molecules.16PubMed. MR appearance of hemorrhage in the brain This staging is particularly useful in forensic and clinical settings where knowing when a bleed started changes the management plan.
Treatment Approaches
Most small, superficial hematomas need nothing more than ice, compression, and time. Applying ice in the first 24 to 48 hours helps limit further bleeding and swelling, and the body handles the rest. For a painful subungual hematoma under a fingernail, the classic treatment is nail trephination: making a small hole in the nail to let the trapped blood escape, which provides near-instant pain relief.
Larger or deeper hematomas sometimes require drainage. A surgeon might aspirate a large intramuscular hematoma with a needle if it is causing pain or restricting movement, or surgically evacuate a hematoma that shows signs of infection. For chronic subdural hematomas in the brain, which are more common in older adults and can develop weeks after a minor head injury, operative options include twist-drill craniostomy, burr-hole craniostomy, and craniotomy, typically reserved for cases where the fluid collection is thick enough to compress the brain or the patient has neurological symptoms.17PubMed. Evidence based diagnosis and management of chronic subdural hematoma: A review of the literature
For retroperitoneal hematomas with active arterial bleeding, the approach is often angiographic embolization, where a catheter is threaded into the bleeding vessel and material is injected to plug the leak, rather than open surgery. This is especially common in pelvic fracture patients where surgical access is difficult and the anatomy is complex.
Chronic Hematomas and Calcification
Not every hematoma resolves cleanly. When the body can’t fully reabsorb a blood collection, the hematoma can become walled off by fibrous tissue and persist for months or years. Chronic subdural hematomas are a textbook example. After an initial bleed, the body forms a membrane around the clot. New, fragile blood vessels grow into this membrane, and those vessels are prone to re-bleeding, which is why chronic subdural hematomas can slowly expand long after the original injury. Research into rebleeding in these hematomas has found that elevated levels of specific enzymes involved in tissue remodeling are associated with repeated bleeding episodes.18PubMed Central. Angiogenetic Factors in Chronic Subdural Hematoma Development
In muscle, an unresolved hematoma can undergo a different kind of transformation. Rather than staying liquid or fibrous, the blood collection can calcify over time, a process related to myositis ossificans, where the body essentially lays down bone-like material in the damaged muscle. This calcification is considered “mature” roughly five months after the initial injury.19PubMed Central. Supraspinatus Intramuscular Calcified Hematoma or Necrosis Associated with Tendon Tear A calcified intramuscular hematoma can cause a hard, palpable lump and restrict joint movement. In some cases, surgical removal is necessary.
Practical Advice for Managing a Hematoma at Home
If you’ve got a garden-variety hematoma from a bump or fall, the management is straightforward. Ice the area for 15 to 20 minutes at a time during the first day or two, with a cloth between the ice and your skin. Compression with a bandage helps limit further swelling, and keeping the injured area elevated reduces blood flow to the site. Over-the-counter pain relief with acetaminophen is a reasonable choice; aspirin and ibuprofen can thin the blood slightly and theoretically worsen the bleed in the early stages, though this matters more for fresh, actively expanding hematomas than for one that’s already starting to change color.
What you should watch for is a hematoma that keeps getting bigger, becomes rock-hard, causes numbness or tingling downstream, or develops warmth and redness suggesting infection. A hematoma on the head after any significant impact warrants medical evaluation, especially in young children and older adults on blood thinners. Similarly, abdominal pain with dizziness or lightheadedness after a fall or procedure could signal a deep hematoma that’s causing significant blood loss internally.
Hematomas After Surgery and Procedures
Postoperative hematomas are one of the most common surgical complications across virtually every specialty. They form when a blood vessel that was sealed during surgery starts leaking again, or when oozing from the raw surgical surface accumulates faster than the body can absorb it. In cardiac catheterization patients, where a large artery in the groin is punctured and later sealed by manual pressure, hematomas at the access site develop in about one in ten cases.20PubMed. Femoral artery complications after cardiac catheterization: a study of patient profile Most are minor, but a small percentage involve active bleeding that requires intervention.
Surgeons manage the risk of postoperative hematomas through careful technique, including meticulous cauterization of small bleeders, layered wound closure, and sometimes the placement of drains to prevent blood from accumulating. Patients are typically advised to avoid heavy lifting or straining in the early postoperative period for this reason. If you notice rapid swelling, increasing firmness, or drainage of dark blood at a surgical site, contacting your surgical team promptly is the right move. Early hematomas that are expanding can often be managed with pressure and observation, but some require a return to the operating room for evacuation and re-hemostasis.
The timing matters, too. A hematoma that forms in the first few hours after surgery is usually from a technical bleeding point. One that shows up days later may reflect a clotting problem, a medication issue, or an infection eroding into a vessel. Each scenario calls for a different response, which is why postoperative swelling that feels abnormal is always worth reporting even if it seems minor.