A hemorrhage is the loss of blood from a damaged blood vessel. It can flow outside the body through a wound or opening (external hemorrhage) or become trapped inside the body in places like the brain, chest, or abdomen (internal hemorrhage). Some hemorrhages are minor, like oozing from a scrape, while others involve rapid, life-threatening blood loss that can send the body into shock within minutes.
How Bleeding Differs by Blood Vessel
Not all bleeding looks or behaves the same way. The type of vessel that’s damaged determines how fast blood escapes and how dangerous the situation is.
Arterial bleeding is the most serious. Arteries carry blood under high pressure directly from the heart, so a damaged artery produces bright red blood that spurts or pulses with each heartbeat. This type of blood loss can become life-threatening very quickly.
Venous bleeding comes from veins, which carry blood back toward the heart at lower pressure. The blood is darker red and flows steadily rather than spurting. It’s easier to control than arterial bleeding but can still be dangerous if a large vein is involved.
Capillary bleeding is the most common type, resulting from damage to the tiny vessels near the skin’s surface. It produces a slow ooze rather than a flow. A scraped knee or minor cut causes capillary bleeding, which usually stops on its own.
What Causes Hemorrhages
Traumatic injury is the most obvious cause. Lacerations, puncture wounds, and crushing injuries can damage any blood vessel. But hemorrhages also happen without any external injury. An aneurysm, which is a weakened, ballooning section of a blood vessel wall, can rupture without warning. High blood pressure weakens vessel walls over time, making spontaneous bleeding more likely, particularly in the brain.
Certain medical conditions raise the risk significantly. Blood clotting disorders prevent the body from sealing damaged vessels efficiently. Liver disease reduces the production of clotting proteins. Medications that thin the blood, including common ones prescribed for heart conditions and stroke prevention, can turn what would be minor bleeding into a serious hemorrhage. Cocaine use is also associated with hemorrhages in the brain, both from aneurysm rupture and from other vascular causes.
How Your Body Tries to Stop Bleeding
The moment a blood vessel is damaged, your body launches a four-stage process called hemostasis. First, the injured vessel constricts, narrowing its diameter to reduce blood flow. This happens within about 30 minutes of the injury. Second, platelets (small cell fragments in your blood) rush to the damaged site and clump together, forming a temporary plug. Third, a chain reaction of clotting proteins activates in your blood, creating a mesh of a tough protein called fibrin. Finally, that fibrin mesh reinforces the platelet plug into a stable clot that seals the wound.
When any step in this process fails, or when the damage is too severe for the body to repair on its own, bleeding continues and the hemorrhage becomes a medical emergency.
Hemorrhages by Location
Brain Hemorrhages
Bleeding inside or around the brain is one of the most dangerous types of hemorrhage. A subarachnoid hemorrhage occurs when blood leaks into the fluid-filled space surrounding the brain. About 85% of non-traumatic cases are caused by a ruptured aneurysm. Other causes include abnormal tangles of blood vessels (arteriovenous malformations), tears in artery walls, and conditions like sickle cell disease. Brain hemorrhages can also occur deeper within the brain tissue itself, often driven by chronic high blood pressure. These account for roughly 10% of all strokes.
Gastrointestinal Hemorrhages
Bleeding in the digestive tract shows up differently depending on where it originates. Upper GI bleeding, from the esophagus, stomach, or upper intestine, can cause vomiting of fresh blood or dark, coffee-ground-like material. It also produces black, tarry, sticky stools with a distinctive odor, known as melena. Lower GI bleeding, from the colon or rectum, typically appears as bright red blood passed during a bowel movement. Occasionally, very rapid upper GI bleeding produces bright red blood from below as well, which can make the source harder to pinpoint.
Postpartum Hemorrhage
Hemorrhage following childbirth is defined as cumulative blood loss of 1,000 mL or more, or any blood loss accompanied by signs of dangerously low blood volume, within 24 hours of delivery. It remains one of the leading causes of maternal death worldwide.
The Four Classes of Blood Loss Severity
The average adult has roughly 5 liters of blood. Medical professionals grade hemorrhage severity into four classes based on how much of that total volume has been lost and how the body is responding.
- Class 1 (up to 15%, about 750 mL): Heart rate, blood pressure, and breathing are essentially normal. This is roughly equivalent to donating blood. The body compensates without much trouble.
- Class 2 (15% to 30%, 750 to 1,500 mL): Heart rate climbs to 100 to 120 beats per minute, and breathing rate increases. Blood pressure may still appear close to normal, but the difference between the upper and lower numbers starts to narrow, an early warning sign.
- Class 3 (30% to 40%, 1,500 to 2,000 mL): Blood pressure drops significantly. Heart rate exceeds 120 beats per minute. Mental status changes, meaning the person may become confused, anxious, or disoriented. Urine output drops because the kidneys aren’t getting enough blood flow.
- Class 4 (over 40%, more than 2,000 mL): Blood pressure is dangerously low. The person may be barely conscious or unresponsive. Urine output is minimal or absent. Without immediate intervention, this stage is fatal.
The transition from Class 2 to Class 3 is where the body’s ability to compensate starts to fail. That’s why changes in mental state and a falling blood pressure together are treated as red flags for hemorrhagic shock, the point at which blood loss is too severe for the body’s organs to receive adequate oxygen.
How Hemorrhages Are Detected
External bleeding is obvious, but internal hemorrhages can be harder to identify. Blood tests provide indirect evidence. A drop in hemoglobin (normally 14 to 17 g/dL in men, 12 to 15 g/dL in women) or hematocrit (normally 41% to 50% in men, 36% to 44% in women) suggests blood loss, though these values don’t always drop immediately because both blood cells and plasma are lost together at first. Platelet counts, normally between 140,000 and 450,000 cells per microliter, help reveal whether a clotting problem is contributing to the bleeding. Imaging, such as CT scans for brain hemorrhages or focused ultrasound for abdominal bleeding, is used to pinpoint the source.
Stopping a Hemorrhage
For external bleeding, direct pressure on the wound is the first and most effective step. Constant, firm pressure against a hard surface should be maintained without lifting to check whether the bleeding has stopped. If the wound cavity is deep and direct pressure alone isn’t working, packing the wound with gauze or hemostatic dressings (materials designed to accelerate clotting) can create internal pressure against the bleeding vessel.
For limb injuries where bleeding can’t be controlled by pressure, tourniquets are a critical tool. Military and civilian emergency guidelines now recommend their early use for life-threatening extremity hemorrhage. Pressure dressings, essentially a tight bandage over a bulky pad, can free up a rescuer’s hands once initial pressure has controlled the flow.
Internal hemorrhages require a different approach entirely. Bleeding inside the chest, abdomen, or pelvis can’t be compressed from the outside. These non-compressible hemorrhages typically require surgery or other procedures to locate and seal the damaged vessel. In the emergency setting, a clot-stabilizing medication may be given intravenously within three hours of injury to help the body’s own clotting mechanisms work more effectively while the source of bleeding is addressed.