Coughing up blood, known medically as hemoptysis, is most commonly caused by acute bronchitis, bronchiectasis (damaged airways), lung infections like pneumonia, or lung tumors. In most cases the amount of blood is small, often just streaks mixed into mucus, and the cause turns out to be a treatable infection or irritation in the airways. But because some causes are serious, any episode of coughing up blood deserves medical attention.
The Most Common Causes
In a study of 606 patients who coughed up blood, the three most frequent diagnoses were lung cancer (19%), pneumonia or lung abscess (19%), and bronchiectasis (15%). Acute bronchitis, one of the most routine respiratory infections, is also a leading cause. These four conditions account for the majority of cases in developed countries.
In parts of the world where tuberculosis is more prevalent, TB and parasitic lung infections are among the top causes instead. The underlying mechanism is similar across most causes: inflammation or infection damages the delicate blood vessels lining the airways, allowing blood to leak into the mucus you cough up.
Infections and Airway Inflammation
Bronchitis, pneumonia, and tuberculosis all inflame the lining of the airways or the lung tissue itself. That inflammation weakens small blood vessels, and the repeated force of coughing can rupture them. With acute bronchitis, you might notice just a few streaks of blood in your phlegm that resolve as the infection clears. Pneumonia and lung abscesses tend to produce more blood because the infection runs deeper into lung tissue, sometimes eroding into larger vessels.
Bronchiectasis is a condition where the airways become permanently widened and scarred, often from repeated infections or conditions like cystic fibrosis. These damaged airways develop fragile, overgrown blood vessels that bleed easily. People with bronchiectasis may experience recurring episodes of bloody mucus over months or years, especially during flare-ups.
Lung Cancer and Tumors
Between 20% and 60% of people with non-small cell lung cancer will cough up blood at some point during their illness. Tumors growing inside or near the airways erode into blood vessels as they expand. In 5% to 10% of lung cancer patients, the bleeding becomes severe. Coughing up blood is sometimes the first symptom that leads to a cancer diagnosis, which is one reason doctors take this symptom seriously even when the amount of blood seems minor.
Weight loss you can’t explain, persistent cough lasting more than a few weeks, chest pain, and night sweats alongside bloody mucus are combinations that raise particular concern for cancer or tuberculosis. A history of smoking significantly increases the likelihood that a tumor is involved.
Blood Clots and Vascular Problems
A pulmonary embolism, a blood clot that travels to the lungs, can cause coughing up blood along with sudden shortness of breath and sharp chest pain. The clot damages pulmonary blood vessels, and the resulting inflammation and tissue injury release blood into the airways. This combination of symptoms, especially after prolonged immobility like a long flight or recovery from surgery, points toward a clot rather than an infection.
Heart conditions that raise blood pressure in the lung’s veins can also force blood out of the vessels and into the airways. This happens in some types of heart failure, where the left side of the heart can’t pump blood forward efficiently, causing pressure to back up into the lungs.
Less Common Causes
Autoimmune diseases can attack the lungs directly. Conditions like Goodpasture syndrome and certain forms of vasculitis damage the tiny blood vessels in lung tissue, causing bleeding that shows up as bloody coughs. These are rare but important to identify because they require specific treatment to stop the immune system from continuing to destroy lung tissue.
Trauma to the chest, blood-thinning medications, and bleeding disorders can all contribute as well. Even a severe, prolonged coughing fit from any cause can occasionally rupture a small airway vessel on its own.
Causes in Children
Children cough up blood far less often than adults, and the causes tend to be different. The most common are respiratory infections (pneumonia, bronchitis, viral illness), foreign body aspiration (inhaling a small object that irritates or damages the airway), and cystic fibrosis. Congenital heart disease with abnormal blood vessel development in the lungs is another possibility unique to pediatric cases. Lung cancer, a major cause in adults, is extremely rare in children.
How to Tell It’s Coming From the Lungs
Blood from the lungs and blood from the stomach can both end up in your mouth, and telling them apart matters because the causes and treatments are completely different. Blood coughed up from the lungs is typically bright red and frothy, often mixed with mucus. Blood vomited from the stomach tends to be darker, sometimes resembling coffee grounds, and may contain food particles. If blood appears after a coughing episode and feels like it’s coming from your throat or chest, it’s more likely from the respiratory tract. If it comes up with nausea or retching, the stomach is the more likely source.
How Doctors Find the Source
A chest X-ray is usually the first step, looking for signs of infection, tumors, or fluid. If the X-ray doesn’t reveal a clear answer, a CT scan provides much more detailed images of the lungs and blood vessels. In some cases, doctors use a bronchoscopy, a thin camera passed through the nose or mouth into the airways, to look directly at the source of bleeding. This is especially useful when bleeding is active or when imaging hasn’t pinpointed the cause.
The blood supply to your lungs comes from two separate systems. The bronchial arteries, which feed the airway walls, are responsible for 90% of life-threatening bleeding episodes despite carrying only about 2% of the lung’s total blood supply. Identifying which vessel is bleeding guides treatment decisions.
When Bleeding Becomes an Emergency
Most episodes involve small amounts of blood, but massive hemoptysis is a medical emergency. Definitions vary, but coughing up more than 150 to 200 mL of blood (roughly half to two-thirds of a cup) in 24 hours is widely considered dangerous. The risk isn’t just blood loss. Blood filling the airways can obstruct breathing, which is the more immediate threat to life.
Signs that bleeding has become an emergency include difficulty breathing, lightheadedness, a rapid heart rate, or coughing up large volumes of bright red blood. These situations require immediate emergency care.
How Severe Bleeding Is Treated
For life-threatening or recurring bleeding, a procedure called bronchial artery embolization is considered the first-line treatment. A specialist threads a thin catheter through a blood vessel to the bleeding artery in the lung and blocks it with tiny particles or coils. This procedure has a technical success rate of about 97% and stops the bleeding clinically in roughly 93% of cases. However, bleeding returns in about 25% of patients over time, sometimes requiring repeat procedures.
The underlying condition still needs treatment. If the bleeding was caused by an infection, antibiotics or antifungals address the root problem. If a tumor is responsible, cancer treatment takes over once the acute bleeding is controlled. For autoimmune causes, medications that suppress the immune response are the foundation of longer-term management.