A brain bleed happens when a blood vessel in or around the brain ruptures or leaks, allowing blood to pool in places it doesn’t belong. The most common cause is chronic high blood pressure, which gradually weakens artery walls over years until they give way. Head trauma is the second major trigger. But several other conditions, medications, and lifestyle factors can also set the stage for bleeding in the brain.
About 13% of all strokes are hemorrhagic, meaning they involve bleeding rather than a blockage. These bleeds are medical emergencies, and understanding what causes them can help you recognize your own risk.
High Blood Pressure: The Leading Cause
Uncontrolled high blood pressure is responsible for more brain bleeds than any other single factor. When blood pushes against artery walls with too much force for too long, those walls weaken, thin out, and can eventually rupture. This process happens silently over years, which is why high blood pressure is often called a “silent killer.” The small, deep arteries inside the brain are especially vulnerable because they branch directly off larger vessels and absorb a lot of pressure.
A hypertensive emergency, defined as a systolic reading above 180 and a diastolic above 110 with signs of organ damage, poses the most acute risk. But you don’t need to be in a crisis for damage to accumulate. Even moderately elevated blood pressure, left unmanaged for years, can set the stage for a bleed. The rupture itself often happens during a moment of sudden pressure increase, like straining, intense exertion, or emotional stress, on top of already weakened vessels.
Head Trauma
A blow to the head can rupture blood vessels instantly. The type of bleed depends on which vessels tear and where the blood collects. An epidural hematoma forms between the skull and the brain’s outermost protective layer. These are almost always caused by direct trauma: car accidents, sports injuries, falls, or violence. A subdural hematoma forms slightly deeper, between the brain’s protective membranes. Subdural bleeds can follow obvious head injuries, but they can also develop from relatively minor bumps, especially in older adults or people on blood thinners.
Trauma-related bleeds don’t always show symptoms right away. An epidural hematoma can cause a person to feel fine for hours before rapidly deteriorating. Subdural bleeds, particularly chronic ones, may develop over days or weeks, producing gradually worsening headaches, confusion, or drowsiness.
Aneurysms and Vascular Malformations
Some people have structural problems in their brain’s blood vessels that make a bleed more likely. A brain aneurysm is a bulge in an artery wall, like a weak spot on an old tire. Most aneurysms never rupture, but when one does, it typically sends blood into the space surrounding the brain, causing a subarachnoid hemorrhage. The hallmark symptom is a sudden, explosive headache often described as the worst of a person’s life.
An arteriovenous malformation (AVM) is a tangle of blood vessels where arteries connect directly to veins, bypassing the normal network of tiny capillaries that slow blood flow. Without that buffer, the walls of the affected vessels face extreme pressure, making them thin and fragile. AVMs can also cause aneurysms to form nearby, adding another rupture risk. Most AVMs are present from birth but may not cause problems until they bleed, sometimes in young adulthood.
Protein Buildup in Aging Blood Vessels
In people over 55, a condition called cerebral amyloid angiopathy (CAA) becomes an increasingly common cause of brain bleeds. Sticky proteins called amyloid gradually deposit along the walls of arteries in the brain, making them stiff and brittle. Over time, these weakened vessels can leak or burst, causing bleeding directly into the brain tissue. CAA is also linked to dementia, and one of its most concerning features is that it tends to cause repeated episodes of bleeding. The major risk factor is simply age: the older you are, the more amyloid accumulates.
Blood Thinners and Anticoagulant Medications
Blood-thinning medications are prescribed to prevent dangerous clots, but they carry an inherent tradeoff. Intracerebral hemorrhage is considered the most dangerous complication of oral anticoagulant treatment. These medications reduce the blood’s ability to clot, so if a small vessel tears or leaks, even from normal wear, the bleeding can continue unchecked rather than sealing itself off quickly.
The risk is highest when blood thinner levels are too high, when patients are also taking other medications that affect clotting, or when blood thinners are combined with other risk factors like high blood pressure or advanced age. Reversal agents now exist for several classes of these medications, which can help stop the bleeding if given early enough. If you take a blood thinner, keeping your blood pressure well controlled is one of the most important things you can do to reduce your hemorrhage risk.
Cocaine, Alcohol, and Other Substances
Cocaine is one of the most well-documented substance-related causes of brain bleeding, particularly in younger adults. It causes brain hemorrhage primarily by spiking blood pressure acutely, sometimes on top of an undiagnosed aneurysm or AVM. Cocaine also constricts blood vessels in the brain, and even its metabolites, which linger in the body for weeks in chronic users, may continue to cause vessel spasm. Combining cocaine with alcohol creates a compound called cocaethylene, which is even more toxic to the heart and blood vessels.
Heavy alcohol use independently raises the risk of hemorrhagic stroke in a dose-dependent way: the more you drink, the higher the danger. A Finnish study of 278 consecutive subarachnoid hemorrhage cases found that men who consumed large amounts of alcohol in the preceding 24 hours had 2.5 to 4.5 times the risk of a brain bleed compared to non-drinkers. For women, the risk was even steeper, reaching 6.5 times higher with heavy intake. Current smoking also independently increased subarachnoid hemorrhage risk in the same study.
Subdural Bleeds Without Major Injury
Not all brain bleeds follow a dramatic event. Subdural hematomas, in particular, can develop without significant trauma. As people age, the brain shrinks slightly, which stretches the small veins bridging the brain’s surface to its outer membranes. This added tension makes them easier to tear, sometimes from something as minor as standing up too quickly or a light bump.
Low blood counts, abnormal blood vessels, and the use of blood thinners further increase this risk. Chronic subdural hematomas are particularly common in elderly adults and can mimic the symptoms of dementia or a slow-developing stroke, with gradual confusion, personality changes, and unsteadiness developing over weeks.
Where the Bleed Happens Matters
A brain bleed’s location shapes both its symptoms and its cause. There are four main types. An intracerebral hemorrhage occurs inside the brain tissue itself and is most commonly caused by high blood pressure or amyloid angiopathy. A subarachnoid hemorrhage involves bleeding in the fluid-filled space surrounding the brain and is most often caused by a ruptured aneurysm. Epidural and subdural hematomas both involve bleeding between the brain and the skull but in slightly different layers, and trauma is the primary driver for both, though subdural bleeds have the widest range of non-traumatic causes.
Recognizing the Symptoms
Most people experiencing a brain bleed report a sudden, severe headache as the first symptom. Beyond that, the signs can include sudden weakness or numbness on one side of the body, slurred speech, confusion, vision loss, difficulty swallowing, nausea and vomiting, loss of balance, seizures, a stiff neck, sensitivity to light, and in severe cases, loss of consciousness. These symptoms overlap significantly with those of a clot-based stroke, and there is no way to tell them apart without brain imaging. Both require immediate emergency care.
CT scans and MRI are both effective at detecting brain bleeds and are largely interchangeable for identifying and classifying hemorrhages. CT is typically used first in emergency settings because it’s fast and widely available. MRI tends to be slightly more sensitive at picking up very small areas of bleeding.