Does COVID Cause Bloody Mucus? And Other Common Causes

COVID-19 can cause bloody mucus, though it does so far less often than it causes cough, fever, or fatigue. Blood-streaked nasal discharge (epistaxis) and blood in coughed-up phlegm (hemoptysis) have both been documented in COVID patients, sometimes as the very first symptom to appear. The relationship is real but layered: the virus itself damages blood vessels and inflames airway tissue, while many of the treatments used in hospitals add their own bleeding risk. COVID is also far from the only explanation for bloody mucus, and most people who notice a red tinge in a tissue are dealing with something much more mundane.

How COVID-19 Can Produce Bloody Mucus

SARS-CoV-2 has a particular affinity for the cells lining blood vessels. The virus triggers swelling and damage to the inner walls of small vessels throughout the body, along with microscopic blood clots and congestion in the tiniest capillaries.

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This vascular damage matters because the nose and lower airways are packed with fragile blood vessels sitting just beneath a thin mucous membrane. When those vessels swell, develop micro-clots, or lose structural integrity, blood can leak into the surrounding mucus. In the nose, this shows up as bloody or rust-colored nasal discharge. Deeper in the lungs, it can appear as blood-streaked phlegm when you cough.

A prospective study comparing patients who arrived at the hospital with nosebleeds to a control group found that about 15 percent of the nosebleed patients tested positive for SARS-CoV-2, compared to roughly 2.5 percent in the control group.

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That gap is significant enough to suggest that nosebleeds aren’t just coincidental during a COVID infection. Coughing up blood is rarer still, but case reports have documented patients whose only presenting symptom was massive hemoptysis that turned out to be COVID-related. In those cases, the bleeding reflects damage deeper in the lung tissue, where inflamed alveoli (the tiny air sacs) can rupture small blood vessels.

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Why Hospitalized COVID Patients Bleed More

If you or someone you know was hospitalized with COVID and developed nosebleeds or bloody sputum during the stay, the treatments themselves likely played a role. Two hospital interventions stand out as risk factors: supplemental oxygen delivered through nasal prongs and blood-thinning medications.

Nasal cannulas push dry, pressurized air directly against the lining of the nose for hours or days at a time. That constant airflow dries out the mucous membrane and can crack the delicate tissue, leading to nosebleeds. A study of COVID-positive ICU patients found that the overall incidence of nosebleeds was about 7 percent, and of those who bled, roughly 78 percent were on supplemental oxygen. For each additional day a patient spent on nasal oxygen, the risk of developing a nosebleed rose by about 7 percent.

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Blood thinners compound the problem. Because COVID-19 promotes clotting throughout the body, most hospitalized patients receive anticoagulant drugs such as low-molecular-weight heparin. While these medications serve a critical purpose, they also make any existing break in the nasal or airway lining bleed more freely and heal more slowly. One Italian hospital documented 30 COVID patients who developed spontaneous nosebleeds while hospitalized, and all of them were receiving both anticoagulants and supplemental oxygen.

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The takeaway for patients recovering at home is reassuring: if you’re managing a mild COVID infection without supplemental oxygen or blood thinners, the odds of significant bloody mucus are much lower than what hospital studies report. A few pink-tinged tissues from a raw, irritated nose during a bad respiratory infection is common regardless of the virus involved.

Everyday Causes That Have Nothing to Do with COVID

Most bloody mucus episodes never make it to a doctor’s office because the cause is obvious and harmless. Before jumping to any viral explanation, it’s worth considering the most frequent culprits.

Dry air is probably the single biggest offender. In winter, heated indoor air drops to very low humidity, and the thin membrane lining the front of the nose dries out and cracks. You blow your nose in the morning and see bright red streaks. A humidifier in the bedroom usually solves this within a few days.

Aggressive nose-blowing during any cold or allergy flare can rupture the small vessels clustered just inside the nostrils, an area so vascular that even minor trauma produces impressive-looking blood. Nose picking, especially in children, targets the same spot. Frequent use of decongestant nasal sprays containing oxymetazoline (the active ingredient in many over-the-counter sprays) compounds the issue. These sprays work by constricting blood vessels, but prolonged or heavy use leads to rebound swelling, tissue changes, and eventually mucosal damage that bleeds more easily.

A deviated nasal septum, where the wall between the nostrils is shifted to one side, creates another chronic setup for bloody mucus. The airflow through the narrower side is faster and more turbulent, drying out the mucous membrane on the deviated side and making recurrent nosebleeds common.

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All of these causes tend to produce bright red blood mixed into clear or white mucus, usually from one nostril, and usually stopping on its own within a few minutes. If that description matches your experience, a respiratory virus is probably not to blame.

Infections Beyond COVID That Cause Bloody Mucus

Any respiratory infection can irritate the airways enough to produce blood-tinged mucus, especially when it triggers prolonged or violent coughing. Acute bronchitis, pneumonia, and severe sinus infections all inflame the lining of the airways, and a hard enough cough can tear a small capillary. This kind of streaky, pinkish sputum during an upper respiratory infection is generally harmless and stops when the cough settles down.

Tuberculosis is a different story. TB has been the most historically feared cause of hemoptysis, and for good reason. The bacterial infection slowly erodes lung tissue and can eat into pulmonary blood vessels, sometimes forming weakened outpouchings in artery walls. If one of those gives way, the result can be massive, life-threatening bleeding.

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TB is uncommon in high-income countries today, but it remains a leading cause of major hemoptysis worldwide, alongside bronchiectasis (permanent dilation of the airways from repeated infections), lung abscess, and fungal lung disease.

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Invasive fungal sinus infections deserve a mention because they can produce bloody nasal discharge that looks alarming and progresses fast. These infections primarily strike people with weakened immune systems, such as those undergoing chemotherapy or organ transplant recipients. Early on, the symptoms mimic an ordinary sinus infection, but the fungus can invade tissue aggressively, causing the mucous membrane inside the nose and sinuses to turn pale or black as it dies. Bloody or foul-smelling nasal discharge in someone who is immunocompromised warrants same-day medical evaluation.

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Blood Clots in the Lungs

Pulmonary embolism, a blood clot that travels to the lungs, is an underappreciated cause of coughing up blood. It doesn’t cause the nasal kind of bloody mucus, but it does produce blood-streaked or rust-colored sputum, and it became particularly relevant during the pandemic because COVID-19 raises clotting risk. Classic descriptions report hemoptysis in roughly a third of patients with pulmonary embolism, typically alongside sudden shortness of breath, chest pain, and a rapid heart rate.

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The hemoptysis from a pulmonary embolism happens because the clot blocks blood flow to a section of lung tissue, causing that tissue to die and the surrounding small vessels to leak. The blood mixes with mucus and comes up when you cough. If you’ve recently been immobilized (long flight, surgery, bed rest), are on hormonal contraceptives, or have a history of clotting disorders, coughing up blood plus sudden breathlessness is a combination that needs emergency evaluation. During and after a COVID infection, the threshold for concern should be even lower, because the virus independently promotes clot formation.

Lung Cancer and Bloody Sputum

This is the possibility most people quietly worry about when they see blood in their sputum, so it’s worth addressing directly. Blood-streaked phlegm is one of the more common early signs of lung cancer. In a large Chinese study of over 6,000 patients diagnosed with non-small cell lung cancer, the most frequent initial symptom was a chronic cough (about 65 percent of patients), followed by sputum with blood at roughly 33 percent.

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That number sounds high, but context matters. Most people who cough up a streak of blood do not have lung cancer. The vast majority have one of the common benign causes already discussed: an infection, dry airways, or irritation from prolonged coughing. The concerning pattern is persistent, unexplained hemoptysis that recurs over weeks, especially in a smoker or former smoker, someone over 40, or a person with unintentional weight loss. A one-time episode of pink sputum during a cold is a fundamentally different clinical picture from repeatedly coughing up blood without an obvious respiratory infection.

If bloody sputum persists for more than a week after other cold or flu symptoms have resolved, or if it’s happening without any infection at all, a chest X-ray or CT scan is a reasonable next step. Early-stage lung cancer is far more treatable than late-stage disease, so this is one situation where being cautious pays off.

Autoimmune Conditions and Alveolar Hemorrhage

A less common but important category involves autoimmune diseases that attack blood vessels in the lungs. The best-known of these is ANCA-associated vasculitis, a group of conditions in which the immune system inflames and damages small blood vessels. When this happens in the lungs, the inflamed vessels can rupture, causing bleeding directly into the air sacs. The result is hemoptysis that can range from mild streaking to life-threatening pulmonary hemorrhage.

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These conditions are uncommon in the general population, but they’re worth knowing about because they tend to present with a constellation of symptoms that can initially be mistaken for a lingering respiratory infection: cough, bloody sputum, fatigue, joint pain, and sometimes kidney involvement. If you’ve been told you have a sinus infection or bronchitis that just won’t clear up, and you’re also noticing bloody urine, unexplained rashes, or numbness in your extremities alongside the bloody mucus, autoimmune vasculitis moves higher on the list of possibilities. Same-day hospital assessment is recommended when hemoptysis appears alongside those other features.

Telling Nasal Blood from Lung Blood

One practical distinction that trips people up is figuring out where the blood is actually coming from. Blood that originates in the nose or sinuses mixes with nasal mucus and typically appears when you blow your nose or drips down the back of your throat (postnasal drip). It’s usually bright red, and you can often feel the irritation or dryness in one nostril.

Blood from the lungs, on the other hand, comes up when you cough. It’s often mixed with frothy or thick sputum and can be bright red, pink, or rust-colored depending on how long it’s been sitting in the airways. Sometimes the two get confused because blood from the nose drains backward into the throat and then gets coughed up, making it look like it came from the lungs. If you’re unsure, paying attention to timing helps: if the blood appears only with nose-blowing and you can see the source inside the nostril, it’s nasal. If it appears only with coughing and there’s no nasal bleeding, it’s more likely from the lower airways.

The distinction matters because the list of possible causes is different. Nasal blood points toward dryness, decongestant overuse, a deviated septum, or sinus infection. Lung blood raises questions about infection, clots, or, less commonly, cancer or autoimmune disease. Your doctor will likely ask you to be specific about which scenario you’re experiencing, so it helps to notice the pattern before your appointment.

When Bloody Mucus Needs Urgent Attention

A few red flags separate the “probably fine” scenarios from the “get to a doctor today” ones:

• Volume: Coughing up more than a teaspoon or two of blood, or blood that’s clearly not just streaks but pools, warrants emergency evaluation.
• Breathlessness: Bloody sputum plus sudden difficulty breathing raises concern for a pulmonary embolism or significant lung hemorrhage.
• Persistence: Blood-tinged mucus that continues daily for more than a week without an obvious cause like a cold or dry air should be investigated.
• Systemic symptoms: Unexplained weight loss, night sweats, or fever lasting weeks alongside bloody mucus need a workup for TB, cancer, or autoimmune disease.
• Immune suppression: If you’re on chemotherapy, immunosuppressive drugs, or have poorly controlled diabetes, even modest bloody nasal discharge could signal an invasive fungal infection that needs rapid treatment.

For most people dealing with a few blood-streaked tissues during a COVID infection or a winter cold, the situation resolves once the infection clears and the irritated mucous membranes heal. Running a humidifier, using saline nasal spray instead of medicated decongestants, and resisting the urge to blow your nose forcefully all speed recovery. The reassuring reality is that the most common causes of bloody mucus are also the most harmless ones, but the exceptions are serious enough that persistent or heavy bleeding deserves professional attention rather than reassurance from the internet.