Internal bleeding happens when a blood vessel is damaged inside your body and blood leaks into surrounding tissues or body cavities where it shouldn’t be. Unlike a visible cut, the blood has nowhere to exit, so it pools around organs, inside the skull, or within the abdomen or chest. The causes range from sudden traumatic injuries to slow, chronic conditions that quietly erode blood vessels over time.
Blunt Force Trauma
Car accidents, falls, sports collisions, and physical assaults are among the most common triggers. When your body takes a hard hit, three distinct forces can damage internal structures.
The first is deceleration. If you’re moving fast and stop suddenly, your organs don’t all stop at the same speed. Structures that are anchored in place, like the aorta attached to the spine, decelerate faster than parts that are more mobile. This mismatch creates shearing forces that can tear blood vessels or rip organs from their attachments. A classic example is an aortic tear during a high-speed car crash.
The second is crushing. Your organs get compressed between the front of your abdomen and your spine or rib cage. Solid organs like the spleen, liver, and kidneys are especially vulnerable because they’re dense and don’t flex easily under pressure.
The third is compression from outside objects. A seatbelt pressing into your abdomen during a collision, for instance, can cause a sudden spike in pressure inside hollow organs like the intestines or bladder, sometimes rupturing them.
Stomach and Intestinal Bleeding
Your digestive tract is lined with a protective mucus layer that shields it from its own acid. When that barrier breaks down, acid eats into the stomach or intestinal wall, forming ulcers. If an ulcer erodes deep enough, it reaches the blood vessels beneath the surface and causes bleeding.
The two biggest drivers of ulcer formation are infection with the bacterium H. pylori and regular use of pain relievers like ibuprofen, naproxen, and diclofenac. These medications reduce inflammation, but they also thin the protective mucus lining of the stomach. The bleeding can be slow, causing gradual anemia over weeks or months, or sudden and severe enough to require hospitalization.
Medications That Raise Your Risk
Blood thinners are the medication class most strongly linked to internal bleeding. They work by reducing your blood’s ability to clot, which is helpful for preventing strokes and heart attacks but leaves you more vulnerable to hemorrhage from even minor injuries.
The risk rises sharply when blood thinners are combined with common over-the-counter painkillers. A large study published in the American Heart Association’s journal Circulation found that people taking oral blood thinners who also started using NSAIDs (ibuprofen, naproxen, diclofenac) had a 61% higher risk of major bleeding compared to those who avoided the painkillers. The most common locations for that bleeding were the upper gastrointestinal tract and, in roughly 15% of major bleeding events, inside the skull. NSAIDs cause damage on two fronts: they irritate the stomach lining directly and they interfere with the blood’s clotting ability.
Aneurysms and Weakened Blood Vessels
An aneurysm is a bulging weak spot in an artery wall. It can sit silently for years, growing slowly, until the wall becomes too thin and ruptures. When it does, blood pours into the surrounding space, and the bleeding can be immediately life-threatening.
The abdominal aorta, the largest artery in the body, is a common site. Smoking is the single strongest risk factor because it directly weakens vessel walls. High blood pressure adds constant mechanical stress, gradually stretching the artery. Atherosclerosis, the buildup of fatty deposits inside artery walls, also contributes by making vessels stiff and fragile. Aneurysms in the brain follow similar principles and can cause a type of stroke called a hemorrhagic stroke when they burst.
Liver Disease and Variceal Bleeding
Chronic liver disease, particularly cirrhosis, creates a dangerous chain reaction. As scar tissue replaces healthy liver tissue, blood can no longer flow through the liver easily. Pressure builds in the portal vein, the major vessel that carries blood from the intestines to the liver. This condition, called portal hypertension, forces blood to find alternate routes through smaller veins that aren’t built to handle the load.
These overloaded veins, called varices, develop most commonly at the base of the esophagus. They become swollen and thin-walled, like overfilled balloons. The risk of a variceal bleed becomes significant once the pressure gradient across the liver exceeds a specific threshold (roughly double the normal level). When a varix ruptures, the bleeding is often massive and rapid, making it one of the most dangerous complications of cirrhosis.
Bleeding Inside the Skull
The brain is uniquely vulnerable because it sits inside a rigid skull with no room to expand. When bleeding occurs inside the skull, pooling blood creates pressure that compresses brain tissue and cuts off oxygen supply to surrounding cells.
Head injuries from falls are the most frequent cause, particularly in older adults and people on blood thinners. Uncontrolled high blood pressure is another major contributor, as it can weaken small arteries in the brain over time until one gives way. Bleeding can occur in several distinct spaces: between the skull and the brain’s outer membrane, between the layers of membrane surrounding the brain, or within the brain tissue itself. Each location produces somewhat different symptoms and timelines, but all are medical emergencies.
How to Recognize Internal Bleeding
The symptoms depend heavily on how much blood has been lost and where the bleeding is occurring. Up to 15% blood volume loss often produces no obvious symptoms at all. This is roughly 750 milliliters, a little less than a full water bottle, in an average adult.
Between 15% and 30% blood loss, the body starts showing signs of strain: dizziness, lightheadedness, a faster heart rate, fatigue, nausea, and shortness of breath. These symptoms reflect your cardiovascular system working harder to compensate for the reduced blood volume.
Beyond 30% blood loss, the situation becomes critical. Confusion, seizures, loss of consciousness, and hypovolemic shock (where the heart can no longer pump enough blood to sustain organs) can follow rapidly.
Location-specific signs can also appear. Abdominal bleeding may cause swelling, bruising around the belly, or blood in vomit, urine, or stool. A brain bleed can produce sudden severe headache, vision changes, weakness on one side of the body, or difficulty speaking.
Why Speed Matters
Internal bleeding, especially from torso injuries, can become fatal faster than many people realize. A large analysis of over 42,000 trauma records found a steep rise in mortality for patients with severe, non-compressible torso hemorrhage when prehospital time exceeded 30 minutes. That’s well before the traditional “golden hour” concept that many people have heard of. The takeaway is straightforward: internal bleeding from trauma is a race against time, and the faster someone reaches a surgical team, the better their odds.
In emergency departments, a rapid ultrasound exam called a FAST scan is typically the first step. It can detect as little as 200 milliliters of free fluid in the abdomen, chest, or around the heart within minutes of arrival. CT scans follow when more detail is needed, particularly for brain bleeds or to pinpoint the exact source of abdominal hemorrhage.