Phlegm is a type of mucus produced in the lungs and lower respiratory tract. It is most noticeable when a person is acutely sick or has a longstanding health condition.
Mucus forms a protective lining in certain parts of the body, even when a person is well. Mucus keeps these areas from drying out and helps to defend against invaders, including viruses and bacteria.
Though a healthy body requires some mucus, too much can be uncomfortable. Excess may be caused by:
- infections, such as the common cold or flu
- irritation of the nose, throat, or lungs
- digestive conditions, such as gastroesophageal reflux disease
- smoking tobacco products