Blood in phlegm with flu: what to know

Influenza may inflame the airways and produce thick mucus; repeated coughing can then break tiny surface blood vessels, leaving fine red or pink streaks. That explanation does not confirm the cause. Pneumonia can develop during or after a viral illness and may bring fever, worsening cough, chest pain, or difficulty breathing. Bronchiectasis, tuberculosis, and other lung problems can also produce blood in sputum, so the wider picture matters.

Rest and drink fluids unless a clinician has advised fluid restriction. Avoid smoking and vaping, and do not strain to clear mucus. Record when the blood appeared, its colour, whether it was mixed through phlegm, and whether fever or breathing symptoms are changing. Contact a clinician promptly, particularly if you are pregnant, older, immunocompromised, or living with heart or lung disease. Take only recommended medicines and follow their dosing instructions.

Seek emergency care for breathlessness at rest, chest pain, confusion, faintness, blue-grey lips, or bleeding that is more than a small streak or keeps returning. Same-day advice is appropriate when fever is worsening, you cannot keep fluids down, your breathing is getting harder, or you are becoming unusually weak. A sudden combination of chest pain and breathlessness needs urgent assessment.

Ask whether this fits airway irritation or suggests pneumonia, whether you need an examination or testing, and how long to monitor the sputum. Ask which flu treatments are suitable for you and what symptoms should trigger emergency help.