Phlegm with blood. A cough with blood is a dangerous condition that may indicate an internal bleeding. Mucus is called a substance that is released during coughing. Sputum contains a secret of bronchial glands, dust particles, and microbes. If in the sputum there are streaks of reddish-pink color, then it has got blood. Sometimes the reason for this is the rupture of a small blood deferent in the lungs – in this case, such event does not pose a significant threat to health. But perhaps, the blood in the sputum signals about infectious processes in the lungs (including lung cancer). If there is such sign more than one week, it is better to consult a doctor as soon as possible.