What is Phlegm? Phlegm (pronounced flem; from Greek phlegma = inflammation) is an informal name for mucus coughed up from the throat. In this article, a term phlegm will be used only for mucus produced in the mucous layer of bronchi and windpipe (trachea). Medical term for phlegm is expectorated matter or sputum. Phlegm appears as thick, jelly-like fluid of various colors and consistency, depending on the cause. Phlegm is composed mainly from water and glycoproteins secreted by mucous glands. Colors of Phlegm Clear phlegm means there is no pus or blood in it. Yellow or green (not translucent) phlegm is mucus mixed with pus. Rusty or brown phlegm may be due to smoking, air pollution, blood or infection. Blood in phlegm may appear as read streaks. Pink phlegm may be from asthma. Frothy phlegm originates from the lungs. Read more about phlegm colors. Symptoms Caused by Phlegm Ask a Doctor Online Now! Phlegm may irritate the lower airways and trigger cough. Cough and constant movements of tinny hairy-like projections (cilia) in the lining of the lower airways push phlegm into the throat, from where it can be coughed up or swallowed. Swallowed mucus is degraded by bowel bacteria that … Continue reading Coughing Up Excessive Phlegm (Mucus, Sputum) from the Throat