Blood in your mucus is usually caused by something minor, most often bronchitis or another respiratory infection that has irritated the lining of your airways. That said, it can also signal something more serious, so the amount of blood, how long it lasts, and what other symptoms you have all matter when figuring out the cause.
The medical term for coughing up blood is hemoptysis. It ranges from faint pink streaks in your phlegm to coughing up significant amounts of bright red blood. Most people who notice it for the first time are understandably alarmed, but understanding the common causes and warning signs can help you figure out your next step.
The Most Common Causes
Bronchitis is the single most frequent reason people cough up blood-streaked mucus. When the bronchial tubes (the airways leading to your lungs) become inflamed from a viral or bacterial infection, the delicate lining can crack and bleed slightly. The result is mucus with thin streaks or specks of blood, especially after hard or prolonged coughing. This type of bleeding is almost always small in volume and resolves as the infection clears.
Pneumonia is another common culprit. A lung infection can produce rust-colored or blood-tinged sputum alongside fever, chest pain, and difficulty breathing. Bronchiectasis, a condition where the airways become permanently widened and prone to mucus buildup, also raises the risk of bloody phlegm and recurrent infections.
Beyond infections, simple mechanical irritation can be responsible. A forceful coughing fit from any cause, even allergies or a dry winter cough, can rupture tiny blood vessels in your throat or airways. In these cases the blood is minimal, bright red, and stops quickly.
Make Sure the Blood Is Coming From Your Lungs
Not all blood you spit out actually comes from your respiratory tract. Blood from the lungs tends to be bright red, frothy (mixed with air bubbles), and comes up when you cough. Blood from your stomach or digestive tract is typically darker, may contain food particles, and is more likely to come up when you vomit rather than cough. The distinction matters because the causes and treatments are completely different.
There’s also a third possibility: the blood is coming from your nose or throat rather than your lungs. Bleeding from the back of your nasal passages can drip down and trigger a cough, mimicking a lung problem. A nosebleed you barely notice, irritated gums, or a sore in your mouth can all put blood in what you spit out. Checking your mouth and nose for obvious sources of bleeding is a useful first step.
Blood Thinners and Other Medications
If you take anticoagulant medications (blood thinners), you’re at higher risk for this symptom. These drugs slow your body’s ability to form clots, which means even minor irritation in your airways can produce noticeable bleeding. Coughing up blood is listed as a sign of excessive bleeding on anticoagulants. If you’re on a blood thinner and notice blood in your mucus, contact your prescribing doctor, as your dosage may need adjustment.
When Blood in Mucus Signals Something Serious
In a small but important percentage of cases, coughing up blood points to a more significant condition. A study of patients presenting with this symptom found that lung cancer accounted for about 7.3% of cases, while pulmonary embolism (a blood clot in the lungs) was present in roughly 2.6%. Those numbers are relatively low, but certain factors raise the odds.
For lung cancer specifically, being 65 or older more than doubled the likelihood. Male sex and a history of diabetes also significantly increased the odds. A long history of heavy smoking is another major risk factor. Lung cancer tends to cause persistent, worsening symptoms rather than a one-time streak of blood, and it often comes with unexplained weight loss, fatigue, or night sweats.
Pulmonary embolism typically arrives suddenly with sharp chest pain, shortness of breath, a rapid heart rate, and sometimes leg swelling or pain on one side. The bloody sputum is just one piece of a larger picture.
Heart conditions can also be responsible, though less commonly. Mitral valve stenosis, a narrowing of one of the heart’s valves, increases pressure in the blood vessels of the lungs and can cause blood-tinged sputum along with shortness of breath, fatigue, and irregular heartbeats.
Symptoms That Demand Urgent Attention
A few red-flag symptoms, when combined with bloody mucus, signal that you need medical care quickly:
- Large volume of blood. Coughing up roughly 100 milliliters (about a third of a cup) in an hour, or 500 milliliters over 24 hours, is considered massive and is a medical emergency.
- Unexplained weight loss, night sweats, or persistent fatigue, which may point to cancer or tuberculosis.
- Shortness of breath at rest or significantly reduced breath sounds in one or both lungs.
- Chest pain combined with difficulty breathing, which can suggest pneumonia or a pulmonary embolism.
- Leg pain and swelling on one side, a classic sign of a deep vein clot that could travel to the lungs.
- A heavy smoking history, which raises the probability of a serious underlying cause.
If your only symptom is a small amount of blood streaking your mucus during an obvious cold or cough, the situation is far less urgent. But if the bleeding recurs over more than a week, increases in volume, or appears without a clear trigger like a respiratory infection, getting evaluated is the right call.
What Happens During a Medical Evaluation
When you see a doctor about blood in your mucus, the evaluation typically starts with questions about how much blood you’ve noticed, how long it’s been happening, and whether it comes up with coughing or vomiting. They’ll ask about your smoking history, medications, recent travel, and any other symptoms like fever, weight changes, or leg pain. A physical exam of your mouth, nose, throat, and chest comes next.
Imaging is the cornerstone of the workup. A chest X-ray is often the first test ordered and can reveal infections, masses, or fluid in the lungs. If the X-ray is inconclusive or if the clinical picture suggests something beyond a simple infection, a CT scan of the chest with contrast dye is the next step. This provides a much more detailed view and can detect blood clots in the pulmonary arteries, small tumors, and structural problems in the airways. Both chest X-rays and CT scans with contrast are considered appropriate initial imaging for this symptom by radiology guidelines.
Blood in Mucus in Children
Children cough up blood far less often than adults, and when they do, the causes tend to be different. Respiratory infections are still the most common reason, but foreign body aspiration (inhaling a small object that lodges in the airway) is a cause that’s unique to younger children. Small objects, food, or even plant material can become stuck in the airways, causing irritation, infection, and bleeding. In reported cases, inhaled grass seeds caused bloody coughing and pneumonia-like symptoms in three out of four affected children. If a young child develops a sudden cough with blood and no signs of infection, an inhaled object should be considered, especially if there was a choking episode.