Phlegm is a liquid secretion produced by the mucous membranes of the upper respiratory tract. It is usually referred to as the sputum that is expelled during coughing.
Phlegm is the term used for mucus when relating to a disease process. During an inflammation of upper respiratory tract mucus gets mixed with bacteria, debris and inflammatory cells which constitute phlegm.
There are many reasons of phlegm. Some of the important ones are:
Excessive yelling or shouting
Illness like flu and cold
DISEASES RELATED TO PHLEGM
Bloody sputum can be due to some serious disease like tuberculosis or some minor disease like bronchitis. Coughing up of blood is always a matter of concern.