A blood clot coughed up from the lungs typically looks bright red and frothy, often mixed with mucus or saliva. It can range from pink to deep red to rust-colored, and most of the time it comes out in small amounts, roughly a teaspoon or less. The texture and shape depend on where the clot formed and how long it sat in your airway before you coughed it up.
Color, Texture, and Size
Fresh blood from the lungs is usually bright red because it’s oxygen-rich. The hallmark feature is a bubbly or frothy appearance, caused by air mixing with blood inside the airways. You’ll often see it streaked through mucus or spit rather than as a solid, standalone clot.
When blood sits in the airway for a while before being coughed out, it darkens. A clot that’s been there for hours may look dark red, maroon, or even brownish. Rust-colored sputum typically means a small amount of blood has dried and mixed with mucus over time. In terms of consistency, smaller clots feel gelatinous, similar to the texture of a thick jelly. Larger ones can be firmer, more rubbery, and hold their shape when they land in a tissue or sink.
Most people cough up amounts small enough to fit on a coin. But occasionally, clots can be surprisingly large. In a well-documented case published in a medical journal, a patient with heart failure coughed up a blood clot that had formed inside the branching airways of the right lung. The clot came out as a perfect cast of the bronchial tree, preserving the shape of each airway branch like a mold. This is rare and extreme, but it illustrates how clots take the shape of whatever space they form in.
How Lung Blood Differs From Other Sources
Not all blood that comes out of your mouth started in your lungs. Blood can travel up from the stomach during vomiting, or drip down from the nose or sinuses into the throat. Telling these apart matters because the causes and urgency are different.
Blood from the lungs tends to be bright red, frothy, and alkaline. You’ll usually cough it up, and it’s often mixed with sputum. Blood from the stomach, by contrast, is typically darker (sometimes resembling coffee grounds), may contain food particles, and is acidic. It comes up with nausea or retching rather than a cough. Blood from a nosebleed that drains backward into the throat usually doesn’t have the frothy quality and often follows obvious nasal congestion, dry air, or nose-blowing.
If you’re not sure where the blood is coming from, pay attention to what triggered it. A coughing episode points toward the lungs. Vomiting points toward the stomach. A sensation of blood dripping down the back of your throat, especially at night, suggests the nose or sinuses.
What Causes Blood Clots in the Lungs
The most common reason people cough up blood is a respiratory infection. Bronchitis, pneumonia, and tuberculosis can all inflame and damage the lining of the airways enough to cause bleeding. When that blood pools and clots before you cough it out, you get a visible clot rather than just streaks.
Beyond infections, other causes include bronchiectasis (a condition where the airways become permanently widened and damaged), lung cancer, blood-thinning medications, and heart failure. Pulmonary embolism, where a blood clot blocks a vessel in the lung, can also cause blood to appear in sputum. In some cases, no clear cause is found even after testing.
When the Amount Matters
A few streaks of blood in your mucus after a bad coughing spell is common with chest colds and usually resolves on its own. But volume is an important signal. Clinicians consider coughing up roughly half a cup of blood (about 150 mL) within 24 hours to be life-threatening. Bleeding at a rate of 100 mL per hour, roughly a third of a cup, is equally dangerous.
That said, even small amounts can be serious in certain people. Someone with limited lung function or an underlying heart condition can be endangered by far less blood, especially if a clot blocks a major airway and interferes with breathing. In one large observational study across five hospitals in Italy, about 30 percent of patients who coughed up blood had moderate amounts (between 20 and 500 mL), and just over 2 percent had severe bleeding above 500 mL.
Warning Signs That Need Immediate Attention
Any amount of coughed-up blood deserves medical evaluation, but certain combinations signal an emergency. Coughing up blood alongside significant shortness of breath, chest pain, lightheadedness, or a rapid heart rate suggests substantial bleeding or airway compromise. If the blood is coming out in large volumes, if you’re coughing up clots repeatedly, or if you feel like you’re struggling to breathe between coughs, that warrants a trip to the emergency room rather than a scheduled appointment.
Fever paired with bloody sputum may point to an active infection like pneumonia or tuberculosis. Unexplained weight loss alongside blood in your cough raises concern for lung cancer, particularly in current or former smokers over 40.
How Doctors Find the Source
The first step is usually a chest X-ray, which can reveal infections, masses, or fluid in the lungs. If the X-ray doesn’t give a clear answer, a CT scan of the chest provides a much more detailed picture and can identify smaller tumors, blood vessel abnormalities, or areas of damaged airway.
When the source still isn’t obvious, or when bleeding is active, doctors use bronchoscopy: a thin, flexible camera threaded through the nose or mouth and down into the airways. This lets them see exactly where the bleeding is coming from and, in some cases, treat it on the spot. Blood tests check for clotting problems and signs of infection. If the pattern of bleeding suggests a blood vessel issue, imaging of the lung’s arteries may also be performed.
The combination of what the clot looks like, how much there is, and what your imaging shows gives your medical team a clear picture of the cause and guides what comes next.