Medically reviewed by Amelia MacIntyre, DO Mucus, a fluid in your upper respiratory system, is usually clear. But a number of health conditions can cause it to turn brown. Also known as brown phlegm ...

or up to eight weeks for pneumonia that is severe. Since debris in the lungs that can't otherwise be removed is coughed up, a cough productive of sputum is very common at this stage. Knowing that the ...

Leibniz Institute of Photonic Technology—Member of the Research Alliance “Leibniz Health Technologies”, Albert-Einstein-Straße 9, 07745 Jena, Germany ...