Coughing up blood, known medically as hemoptysis, means that blood is coming from somewhere in your lungs or airways. It can range from a few streaks of blood mixed into your mucus to larger amounts of bright red blood. Most of the time, small amounts come from something treatable like a chest infection or bronchitis. But because coughing up blood can also signal serious conditions like lung cancer or severe lung disease, it always warrants medical attention.
How to Tell the Blood Is From Your Lungs
Blood that comes from the lungs is typically bright red and frothy, often mixed with spit or mucus. It feels like it rises up with a cough rather than coming up with a retch or vomit. Blood that comes from your stomach, by contrast, tends to be darker, sometimes resembling coffee grounds, and may have bits of food mixed in.
Sometimes what looks like coughed-up blood actually started somewhere else. A nosebleed draining down the back of your throat, bleeding gums, or a cut in your mouth can all trigger a cough and make you think the blood came from your lungs. If you’re not sure, pay attention to whether the blood appeared after a coughing spell or after vomiting, and whether it’s bright red or dark. That distinction helps your doctor figure out where to look.
The Most Common Causes
In countries with good access to healthcare, the three most common reasons people cough up blood are acute bronchitis, bronchiectasis (a condition where the airways become permanently widened and damaged), and lung tumors. A study of 606 patients across five Italian hospitals found that cancer accounted for 19% of cases, pneumonia or lung abscess for another 19%, and bronchiectasis for 15%.
Here are the main categories of causes:
- Infections: Bronchitis, pneumonia, tuberculosis, and fungal infections can all inflame or damage the airways enough to cause bleeding. Bronchitis is the single most common cause of mild, short-lived blood in the sputum.
- Bronchiectasis: When the airways are chronically stretched and scarred, often from repeated infections, they become fragile and bleed more easily. This is one of the top causes of both minor and severe bleeding episodes.
- Lung cancer: Tumors growing in or near the airways can erode into blood vessels. Hemoptysis is sometimes the first noticeable symptom of lung cancer, particularly in smokers over 40.
- Blood clots in the lung: A pulmonary embolism can cause coughing up blood along with sudden chest pain and shortness of breath.
- Blood-thinning medications: Anticoagulants like warfarin and newer options like apixaban can make bleeding more likely throughout the body, including in the lungs. Taking NSAIDs like ibuprofen alongside these medications can raise the risk further.
In parts of the world where tuberculosis is still common, TB is one of the leading causes. The underlying condition matters a great deal for treatment, which is why doctors don’t just treat the bleeding itself but work to find out why it’s happening.
Why Lungs Bleed
Your lungs have two separate blood supplies. The pulmonary arteries carry low-pressure blood through the lungs to pick up oxygen. The bronchial arteries, a much smaller system, feed the airway walls themselves and operate at the same high pressure as the rest of your body’s circulation. Even though the bronchial arteries supply only about 2% of the lung’s total blood flow, they’re responsible for roughly 88% of serious bleeding episodes.
This happens because chronic inflammation, repeated infections, or tumors can cause new, fragile blood vessels to sprout from the bronchial arteries. These abnormal vessels are weak-walled and prone to rupturing. In some cases, connections form between the high-pressure bronchial system and the low-pressure pulmonary system, which can make bleeding even harder to control.
When Blood in Your Cough Is an Emergency
A few streaks of blood in your mucus during a bad cold is common and usually resolves on its own. But certain situations call for immediate emergency care. The volume of blood matters: coughing up more than about 100 milliliters in 24 hours (roughly a third of a cup) can be life-threatening, primarily because blood filling the airways can interfere with breathing rather than because of blood loss itself.
Seek emergency care if you experience any of the following alongside coughing up blood:
- Difficulty breathing or shortness of breath at rest
- Chest pain
- Large amounts of blood (more than a few teaspoons)
- Blood that won’t stop after a few minutes
- Lightheadedness, rapid heart rate, or feeling faint
Other warning signs that point to a serious underlying problem, even without a dramatic bleed, include unexplained weight loss, persistent fatigue, back pain, or a long history of heavy smoking. These symptoms together raise the concern for cancer or advanced lung disease.
How Doctors Find the Source
The first step is almost always a chest X-ray. It’s fast, inexpensive, and can reveal pneumonia, masses, abscesses, or other visible abnormalities. But a normal chest X-ray doesn’t rule everything out, since small tumors and some vascular problems won’t show up on a standard film.
If the X-ray doesn’t explain the bleeding, the next step is usually a CT scan of the chest with contrast dye injected into a vein. CT is better than X-ray at pinpointing both the cause and the exact location of bleeding. It can identify abnormal arteries that might be the source, detect blood clots in the lung, and find tumors too small for a plain X-ray to catch.
A bronchoscopy, where a thin flexible camera is passed through the nose or mouth into the airways, is sometimes used alongside or instead of CT. It lets doctors directly visualize the inside of the airways, take tissue samples for biopsy, and even treat active bleeding during the same procedure. CT tends to be better at identifying what’s causing the bleeding, while bronchoscopy is better at catching problems on the airway surface itself. In many cases, doctors use both.
The Link Between Hemoptysis and Lung Cancer
One of the biggest fears people have when they cough up blood is cancer, and while most cases turn out to be something less serious, the concern isn’t unfounded. Among patients whose initial workup finds no clear cause, about 4% are diagnosed with lung cancer within the next three years. That number jumps to 10% for smokers over age 40.
Even among patients initially diagnosed with a respiratory infection as the cause, roughly 10% were later found to have lung cancer within three years of follow-up, based on a large French study using national hospital data. This is why doctors often recommend follow-up imaging even after a seemingly straightforward explanation, especially for patients with risk factors like smoking, older age, or a family history of lung cancer. When lung cancer does cause hemoptysis, the average time between the first symptom and a confirmed diagnosis is about three to four weeks.
How Bleeding Is Treated
Treatment depends entirely on the cause and severity. For mild bleeding from bronchitis, treating the infection and waiting is often enough. Pneumonia-related bleeding improves as the infection clears with antibiotics. If a blood-thinning medication is the culprit, your doctor may adjust the dose or switch to a different drug.
For severe or life-threatening bleeding, a procedure called bronchial artery embolization is often the first-line emergency treatment. A specialist threads a thin catheter through a blood vessel to reach the bronchial artery that’s bleeding, then injects tiny particles to block it off. This procedure has an immediate success rate of 70 to 99%, with complications occurring in fewer than 0.1% of cases. The catch is that bleeding comes back in 10 to 57% of patients over time, depending on the underlying disease, so it often buys time for more definitive treatment.
When the cause is a tumor or a severely damaged section of lung, surgery to remove part of the lung may be necessary. For bleeding caused by bronchiectasis, long-term management focuses on controlling infections and reducing inflammation to prevent future episodes.