It is a juicy secretion in the airway during disease and inflammation; it usually contains mucus with virus, bacteria, other debris, and sloughed-off inflammatory cells.

There are multiple factors that can contribute to an excess of phlegm in the throat or larynx.
• Vocal abuse; clearing the throat; yelling/screaming; nodules.
• Smoking
• Illness: flu, cold, pneumonia, acute bronchitis, tuberculosis and lung cancer (bloody sputum)
• Hay fever, asthma
• Air pollution

Phlegm and mucus are not the same.
- Phlegm is more related to disease than is mucus and can be troublesome for the individual to excrete from the body; once it has been expectorated by a cough it becomes sputum.
- Mucus is a normal protective layering around the airway, eye, nasal turbinate, and urogenital tract. It is an adhesive viscoelastic gel produced in the airway.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on January 2, 2019.