Internal bleeding happens when blood leaks from damaged blood vessels but stays trapped inside the body, pooling in organs, body cavities, or tissues. The causes range from obvious physical injuries to conditions you might not suspect, like common medications or inherited blood disorders. Understanding the full spectrum of causes helps you recognize when something serious may be happening beneath the surface.
Blunt Force Trauma and Deceleration Injuries
Physical trauma is the most straightforward cause. Car accidents, falls, sports collisions, and direct blows to the body can rupture organs or tear blood vessels without breaking the skin. The abdomen is especially vulnerable because the spleen, liver, and intestines sit behind relatively thin muscle walls with no bony protection. In car crashes, the sudden deceleration can cause organs to shift and tear away from their blood supply, even when there’s no visible bruising on the outside.
The spleen and liver are the organs most commonly injured in blunt abdominal trauma. The spleen, in particular, is fragile and blood-rich, making it prone to rupture. In some cases, a damaged spleen develops a delayed rupture, bleeding hours or even days after the initial injury. This is why emergency teams evaluate the mechanism of injury carefully, including vehicle speed and whether alcohol was involved, to avoid missing damage that isn’t immediately obvious.
Stomach and Intestinal Bleeding
The gastrointestinal tract is one of the most common sites for internal bleeding that isn’t caused by trauma. Peptic ulcers, which are open sores in the lining of the stomach or upper small intestine, account for a large share of these cases. About 10 to 20% of people with peptic ulcer disease develop complications, and hemorrhage is by far the most frequent one. Large ulcers on the back wall of the upper small intestine are particularly dangerous because they can erode into a major artery running behind the intestinal wall.
Other gastrointestinal sources include tears in the esophagus (often from violent vomiting), abnormal blood vessel clusters in the intestinal lining, inflammatory bowel disease, and cancers anywhere along the digestive tract. The bleeding can be slow and chronic, causing anemia over weeks or months, or sudden and severe enough to cause vomiting blood or passing dark, tarry stools.
Aneurysms and Weakened Blood Vessels
An aneurysm is a balloon-like bulge in a blood vessel wall. As it stretches, the wall thins, and if it ruptures, blood pours into the surrounding tissue. The two most dangerous locations are the aorta (the body’s largest artery, running through the chest and abdomen) and the arteries supplying the brain.
A ruptured abdominal aortic aneurysm can cause massive, life-threatening blood loss within minutes. Aneurysms closer to the heart face greater blood pressure with each heartbeat, which increases their rupture risk. Brain hemorrhage from a ruptured cerebral aneurysm carries a 30-day fatality rate of roughly 40%, and long-term survival drops sharply with age. Among people aged 75 to 94, ten-year mortality after a brain hemorrhage reaches 90%.
Medications That Increase Bleeding Risk
Blood-thinning medications are a significant and often underappreciated cause of internal bleeding. Warfarin and similar anticoagulants work by slowing your body’s clotting process, which means even minor vessel damage that would normally seal itself can continue to bleed.
The risk climbs substantially when blood thinners are combined with common pain relievers. Taking warfarin alongside an over-the-counter anti-inflammatory like ibuprofen or naproxen nearly doubles the risk of gastrointestinal bleeding compared to warfarin alone. Even prescription anti-inflammatory drugs designed to be gentler on the stomach produce a similar increase in risk when combined with warfarin. This is why anyone on blood thinners needs to be careful about which pain medications they use, even ones available without a prescription.
Blood Clotting Disorders
Some people bleed internally because their blood simply doesn’t clot the way it should. Hemophilia, the most well-known clotting disorder, involves a deficiency in one of the proteins needed to form stable blood clots. People with severe hemophilia can bleed into their joints and muscles spontaneously, without any injury at all. Repeated joint bleeds cause progressive damage over time.
Von Willebrand disease is actually more common than hemophilia, though it’s often milder. It involves a problem with a protein that acts like glue, helping platelets stick together at an injury site. When this protein is missing or defective, clots take longer to form and bleeding takes longer to stop. Most people with von Willebrand disease experience relatively manageable symptoms like heavy periods or prolonged bleeding after dental work. But the most severe form, type 3 (affecting about 3% of people with the condition), can cause bleeding into joints and internal organs that resembles hemophilia.
Ectopic Pregnancy
In an ectopic pregnancy, a fertilized egg implants outside the uterus, most commonly in a fallopian tube. As the pregnancy grows, it stretches the tube until it ruptures, causing internal bleeding that can become life-threatening quickly. Early symptoms often include one-sided lower abdominal pain and vaginal spotting. If the tube ruptures, the pain becomes more widespread and severe, sometimes accompanied by dizziness, fainting, or shoulder pain (a sign that blood is irritating the diaphragm).
The danger with ectopic pregnancy is that early symptoms can mimic a normal early pregnancy or menstrual cramps, which delays diagnosis. A delayed rupture leads to blood pooling in the pelvis and abdomen, causing rapid drops in blood pressure and heart rate changes that signal dangerous blood loss.
Postoperative Bleeding
Surgery itself can cause internal bleeding in the hours or days that follow. The most common reason is incomplete sealing of blood vessels during the original procedure. A suture can slip off a short vessel stump, or a diseased vessel wall may be too rigid for sutures to close it completely. Bleeding can also come from staple lines where sections of intestine were reconnected, or from incidental injuries to the spleen or liver that went unnoticed during the operation.
In some cases, the issue isn’t a single leaking vessel but widespread oozing from raw tissue surfaces. This diffuse bleeding is harder to control and often signals an underlying problem with the body’s clotting system, sometimes triggered by the stress of surgery itself, large blood transfusions, or a drop in body temperature during a long procedure.
How Internal Bleeding Shows Up on the Body
Internal bleeding isn’t always invisible from the outside. When blood pools inside the abdomen, it can eventually seep into the surrounding tissues and produce distinctive discoloration patterns on the skin. Bruising around the belly button (known as Cullen sign) points to bleeding in the abdominal cavity. Bruising along the flanks, which can appear red, purple, yellow, or green depending on how long the blood has been breaking down, indicates bleeding behind the abdominal organs or in the deeper abdominal wall.
These skin signs can appear with a wide range of conditions: severe pancreatitis, a ruptured aortic aneurysm, a ruptured ectopic pregnancy, splenic rupture, or bleeding complications from anticoagulant medications. They typically develop hours to days after the bleeding starts, so their appearance means bleeding has been going on for some time. Less commonly, bruising in the upper thigh or scrotum can also signal abdominal or pelvic hemorrhage tracking downward through tissue planes.
How Internal Bleeding Is Detected
In emergency settings, the fastest way to check for internal bleeding is an ultrasound scan that takes just a few minutes. It examines four specific areas: the space between the liver and right kidney, the area around the heart, the space between the spleen and left kidney, and the pelvis. The scan looks for fluid where there shouldn’t be any. It’s not perfect for detecting small amounts of bleeding, but it’s fast enough to guide immediate decisions about whether someone needs surgery.
CT scans provide much more detailed images and can pinpoint exactly where bleeding is coming from, how much blood has accumulated, and whether it’s still active. For slower or chronic internal bleeding, like a gradually leaking ulcer, blood tests showing a dropping red blood cell count over time may be the first clue.