Coughing up blood, known medically as hemoptysis, happens when blood vessels in the lungs or airways are damaged, inflamed, or ruptured. The four most common causes are bronchiectasis (20%), lung cancer (19%), bronchitis (18%), and pneumonia (16%), which together account for roughly three-quarters of all cases. The amount of blood can range from faint streaks in your mucus to large volumes that require emergency care.
How Blood Enters Your Airways
Two separate sets of arteries supply blood to your lungs. When either system is disrupted by infection, inflammation, or structural damage, blood can leak into the airways and get coughed up. Chronic infections like tuberculosis can also cause new, fragile blood vessels to grow into diseased tissue. These makeshift vessels are weak-walled and prone to rupturing, sometimes producing sudden, heavy bleeding.
Infections That Cause It
Respiratory infections are the single most common trigger. Acute bronchitis inflames the lining of your airways enough to cause small amounts of bleeding, usually showing up as blood-streaked mucus. Pneumonia does the same but at a deeper level, damaging the tiny air sacs where oxygen exchange happens. Both typically resolve once the infection clears.
Tuberculosis deserves special attention. Even after successful treatment, TB can leave behind scarred, distorted lung tissue with weakened blood vessels. One specific complication is a bulge that forms in an artery wall next to an old TB cavity. If that bulge ruptures, it can cause sudden, heavy bleeding. People with a history of TB who notice blood in their cough should take it seriously, even years after treatment.
Bronchiectasis
Bronchiectasis is permanent widening and scarring of the airways, usually from repeated infections. It’s the single most frequent cause of coughing blood in studies of patients referred to hospitals. The damaged airways become chronically inflamed, and the blood vessels feeding them enlarge and become fragile over time. Flare-ups of infection in these damaged airways often trigger bleeding episodes. In children, cystic fibrosis is a leading cause of bronchiectasis, with major bleeding episodes occurring in roughly 1% of affected kids, at an average age of around 15.
Lung Cancer
Lung cancer accounts for about 19% of hemoptysis cases. Tumors growing in the airways can erode into blood vessels, causing bleeding that may start as minor streaks and worsen over time. Coughing blood is sometimes the first noticeable symptom, particularly in current or former smokers. Even when an initial chest X-ray looks normal, doctors will often pursue further imaging if the patient has risk factors for cancer, such as a long smoking history or age over 40.
Heart Problems
Not all causes originate in the lungs. A narrowed mitral valve in the heart (mitral stenosis) raises blood pressure in the veins draining the lungs. That back-pressure can force fluid and blood into the air sacs, leading to blood-tinged or pink, frothy sputum. Heart failure can produce the same effect. In these cases, the bleeding is a sign of fluid overload in the lungs rather than direct airway damage.
Blood Thinners and Medications
If you take anticoagulants (blood thinners) or antiplatelet drugs like aspirin, you have a higher risk of bleeding throughout the body, including the lungs. These medications don’t cause the initial vessel damage, but they make it harder for your body to stop even minor bleeding once it starts. Certain antibiotics and antifungal medications can intensify the effect of blood thinners by changing how your body processes them, further raising bleeding risk. If you’re on a blood thinner and start noticing blood when you cough, that’s worth reporting to whoever prescribes your medication.
Inhaled Drugs and Toxins
Smoking crack cocaine or inhaling amphetamines can cause acute lung injury with sudden coughing of blood, shortness of breath, and rapid heart rate. This is sometimes called “crack lung,” a recognized syndrome involving direct chemical damage to the airways and lung tissue. The damage can happen in both younger and older users, and the bleeding can be significant enough to mimic more common emergencies like a pulmonary embolism. Inhaled heroin and nitrous oxide have also been linked to lung injury.
How to Tell It’s Coming From the Lungs
Blood from the lungs and blood from the stomach can look similar, and it’s common to confuse the two. A few features help distinguish them. Blood coughed up from the airways is typically bright red and foamy, mixed with air bubbles because it has traveled through your breathing passages. Blood vomited from the stomach tends to be darker, sometimes resembling coffee grounds, and comes with nausea rather than a cough. A nosebleed that drains down the back of your throat can also mimic the sensation of coughing up blood, though most people recognize the nosebleed is happening.
What Happens During Evaluation
A chest X-ray is the standard first step for anyone coughing blood who is otherwise stable. It can reveal infections, masses, or fluid buildup that point toward a cause. If the X-ray shows something abnormal, or if there are risk factors for cancer, a CT scan provides a more detailed look and can pinpoint where the bleeding is coming from. In some cases, a camera is passed into the airways (bronchoscopy) to directly visualize the bleeding source.
For heavy or persistent bleeding, a specialized scan called CT angiography maps the blood vessels supplying the lungs. This is often done as a step before a procedure to block the bleeding vessel from the inside, which stops the hemorrhage without surgery.
When It Becomes an Emergency
Small amounts of blood-streaked mucus during a bad chest cold are common and usually not dangerous. The situation changes when the volume increases. Massive hemoptysis is generally defined as coughing up 100 milliliters or more of blood in 24 hours, roughly a half cup, though some definitions use higher thresholds. At these volumes, the danger is less about blood loss and more about blood flooding the airways and blocking breathing. Historical surgical series have reported mortality rates around 13% for massive hemoptysis requiring intervention. Any amount of blood that feels like more than streaks, that keeps coming, or that makes it hard to breathe warrants immediate medical attention.