Phlegm

Phlegm (pronounced ) is sticky fluid secreted by the mucus membranes of humans and other animals. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing (sputum). Its composition varies, depending on climate, genetics and state of the immune system, but basically is a water-based gel consisting in glycoproteins, immunoglobulins, lipids, etc.

In Hippocratic medicine, for hundreds of years until about the 19th century, phlegm was counted as one of the four bodily humours, possessing the properties of coldness and wetness, and was responsible for apathetic and sluggish behaviour. This old belief is preserved in the word phlegmatic.

Humourism is an ancient theory that the human body is filled with four basic substances, called the four humours, which are held in balance when a person is healthy. It states that all diseases and disabilities result from an excess or deficit in black bile, bile, phlegm, and blood.