What Triggers a Hematoma? Understanding the Causes and Risk Factors

September 23, 2025 •

4 min read

According to the Cleveland Clinic, a hematoma is a closed wound where blood collects and fills a space inside your body, often after an injury. Understanding what triggers a hematoma is crucial for knowing when to seek medical care, as not all are harmless. This guide explores the common and less obvious causes.

Quick Summary

A hematoma is triggered primarily by damage to blood vessels, most often from physical trauma like injuries, fractures, or surgery. Underlying medical conditions such as blood clotting disorders, liver disease, and certain medications like blood thinners also significantly increase the risk.

Key Points

Trauma is the main cause: Injuries from falls, accidents, or sports are the most common triggers for a hematoma.
Medications increase risk: Blood-thinning drugs (anticoagulants, antiplatelets) and some NSAIDs can significantly increase your risk of developing a hematoma.
Chronic conditions are a factor: Bleeding disorders, liver disease, and high blood pressure impair clotting and weaken blood vessels, making hematomas more likely.
Not all are harmless: Hematomas in critical areas like the skull can be life-threatening and require immediate medical care.
Aging increases vulnerability: As skin and vessels become more fragile with age, older adults are more susceptible to hematomas from minor trauma.
Location is key: Depending on where it forms (e.g., under the skin, in muscle, or brain), a hematoma can have vastly different levels of severity and symptoms.
Bruise vs. Hematoma: A hematoma involves larger, deeper blood vessel damage, often forming a noticeable lump, distinguishing it from a flat bruise.

Understanding Hematoma Formation

A hematoma forms when blood escapes from a damaged blood vessel, such as an artery, vein, or capillary, and collects in the surrounding tissue. The body's natural response to stop the bleeding is hemostasis, where blood clots begin to form. If the damage is extensive or the bleeding is significant, the blood pools and clots, creating a lump-like mass. Unlike a bruise, which is usually a flat area of discoloration from smaller vessel damage, a hematoma can be larger, deeper, and more painful.

The Role of Trauma and Injury

Trauma is the leading cause of hematoma formation. The impact damages blood vessel walls, causing internal bleeding. The severity of the trauma directly correlates with the size and seriousness of the hematoma. Common traumatic events include:

Blunt force trauma: This can be from a fall, a sports injury, or a motor vehicle accident, where impact crushes tissues and ruptures vessels without breaking the skin.
Penetrating injuries: Gunshot wounds or stabbings can cause damage to larger vessels, leading to significant hematoma development.
Bone fractures: A broken bone can tear or puncture nearby blood vessels, causing extensive bleeding and a hematoma to form.
Medical procedures: Surgical interventions, injections, or vascular catheterizations can sometimes damage vessels, resulting in a post-procedural hematoma.

Medical Conditions That Increase Risk

Beyond direct physical injury, several medical conditions can make a person more susceptible to developing a hematoma, even with minimal trauma.

Bleeding Disorders (Coagulopathy): Conditions like hemophilia and von Willebrand disease impair the blood's ability to clot effectively, increasing the risk of uncontrolled bleeding and hematoma formation.
Liver Disease: The liver produces many of the body's clotting factors. Significant liver disease, such as cirrhosis, can disrupt this production, leading to a higher risk of bleeding.
Vascular Abnormalities: Weakened or malformed blood vessels, like those in an aneurysm, can rupture spontaneously or with less force than normal, triggering a hematoma.
High Blood Pressure (Hypertension): Persistent high blood pressure can weaken vessel walls over time, increasing the risk of rupture, particularly in the brain.

Medications and Aging

Certain medications and the natural process of aging are significant risk factors for hematomas.

Impact of Medications

Medications that interfere with the blood's clotting ability are a major trigger. The risk is elevated for those taking:

Anticoagulants: Also known as blood thinners (e.g., warfarin, heparin), these are prescribed to prevent blood clots but make it easier for hematomas to form from injuries.
Antiplatelet Drugs: Drugs like aspirin and clopidogrel prevent platelets from sticking together. While useful for preventing heart attacks and strokes, they increase bleeding risk.
NSAIDs: Long-term or heavy use of non-steroidal anti-inflammatory drugs like ibuprofen can also affect blood clotting.

Effects of Aging

With age, the skin becomes thinner and blood vessels become more fragile. This means even a minor bump that wouldn't affect a younger person can cause a hematoma in an older adult.

Hematoma vs. Bruise: A Comparison


Feature	Hematoma	Bruise (Contusion)
Cause	Damage to larger blood vessels, pooling of clotted blood.	Rupture of small capillaries near the skin's surface.
Appearance	Often a raised, swollen, and firm lump; may change color.	Flat, discolored patch that changes color as it heals.
Location	Can be superficial (under the skin) or deep (in muscles, organs, or brain).	Usually superficial, on or just under the skin.
Feeling	Tends to be more painful and tender to the touch due to pressure.	Typically less painful than a hematoma.
Healing Time	Can take weeks or even months to resolve, depending on size and location.	Typically fades within a couple of weeks.

Location Matters: Types of Hematomas

The location of a hematoma is a critical factor in determining its severity. Here are some examples:

Subcutaneous Hematoma: The most common type, occurring just under the skin. It often results from minor bumps or medical injections and is usually harmless.
Intramuscular Hematoma: A collection of blood within the muscle tissue, often caused by vigorous physical activity or sports injuries. It can cause significant pain, swelling, and reduced mobility.
Intracranial Hematoma: Occurs inside the skull or brain. This is a medical emergency as pooled blood can increase pressure on the brain, leading to permanent damage or death. Examples include epidural and subdural hematomas.
Subungual Hematoma: Forms under a fingernail or toenail, usually after a crush injury. It causes intense, throbbing pain due to pressure in a confined space.

When to Seek Medical Attention

Most minor, superficial hematomas can be managed at home using the RICE method (rest, ice, compression, elevation). However, certain symptoms warrant immediate medical care. You should consult a doctor if:

The hematoma is large, painful, or expands rapidly.
It appears after a head injury and is accompanied by symptoms like severe headache, confusion, nausea, or slurred speech.
You develop frequent or unexplained bruising and hematomas.
The hematoma causes numbness, weakness, or loss of function in a limb.
For further reading on hematoma management, you can consult an authoritative source like the Cleveland Clinic.

Conclusion

In conclusion, what triggers a hematoma is the rupture of blood vessels, often from trauma, but also from underlying medical issues or the use of specific medications. The key to effective management is correctly identifying the cause and location. While many superficial hematomas resolve on their own, more serious ones require prompt medical evaluation to prevent complications. Being aware of the risk factors and warning signs empowers individuals to make informed health decisions.

Frequently Asked Questions

A hematoma is a larger, deeper collection of blood from a broken blood vessel that often forms a lump. A bruise, or contusion, is typically more superficial, caused by smaller capillaries breaking near the skin's surface and is usually flat.

Yes. While trauma is the most common cause, a hematoma can also form spontaneously due to underlying conditions like bleeding disorders, liver disease, or as a side effect of certain medications.

Intracranial hematomas, which occur in or around the brain, are the most serious. These include epidural and subdural hematomas and can cause significant pressure on the brain, requiring immediate medical attention.

You should seek medical attention if a hematoma is growing rapidly, is accompanied by severe pain, or if you experience neurological symptoms like severe headache, confusion, or weakness, especially after a head injury.

Medications like anticoagulants and antiplatelets inhibit the blood's ability to clot. This means that even a minor injury to a blood vessel can result in excessive bleeding and a larger, more persistent hematoma.

Yes. As people age, their skin becomes thinner and their blood vessels become more fragile. This makes older adults more susceptible to developing hematomas, even from minor bumps or trauma.

Yes, vigorous physical activity or contact sports can lead to an intramuscular hematoma by causing damage to muscle tissue and blood vessels, particularly from direct impact or strain-related injuries.

Yes, high blood pressure can weaken the walls of blood vessels over time. In rare cases, this can lead to a spontaneous rupture, which is a particularly dangerous trigger for an intracranial hematoma.