Phlegm

Phlegm (/ˈflɛm/; Ancient Greek: φλέγμα, phlégma, "inflammation", "humour caused by heat") is mucus produced by the respiratory system, excluding that produced by the throat nasal passages. It often refers to respiratory mucus expelled by coughing, otherwise known as sputum. Phlegm, and mucus as a whole, is in essence a water-based gel consisting of glycoproteins, immunoglobulins, lipids and other substances. Its composition varies depending on climate, genetics, and state of the immune system. Its color can vary from transparent to pale or dark yellow and green, from light to dark brown, and even to dark grey depending on the contents. The body naturally produces about 1 quart (about 1 litre) of phlegm every day to capture and clear substances in the air and bacteria from the nose and throat.

Contrary to popular misconception and misuse, mucus and phlegm are not always the same.

Mucus is a normal protective layering around the airway, eye, nasal turbinate, and urogenital tract. Mucus is an adhesive viscoelastic gel produced in the airway by submucosal glands and goblet cells and is principally water. It also contains high-molecular weight mucous glycoproteins that form linear polymers.

Phlegm is more related to disease than mucus, and can be troublesome for the individual to excrete from the body. Phlegm is a thick secretion in the airway during disease and inflammation. Phlegm usually contains mucus with virus, bacteria, other debris, and sloughed-off inflammatory cells. Once phlegm has been expectorated by a cough, it becomes sputum.

There are multiple factors that can contribute to an excess of phlegm in the throat or larynx.

Phlegm naturally drains down into the back of the throat and can be swallowed without imposing health risks. Once in the stomach, the acids and digestive system will remove the phlegm and get rid of the germs in it. In some cultures, swallowing phlegm is considered a social taboo, being described as disgusting or unhygienic. One Igbo adage, for example, uses the swallowing of phlegm as a metaphor for wrongdoing. Also, due to the social image of spitting (the alternative of swallowing) in some communities, females were shown to be more likely to swallow phlegm and less likely to report experiencing it.

The alternative to swallowing would be throat-clearing. To do this, the mouth should be closed and air should be inhaled hard into the nose. Inhaling forcefully through the nose will pull excess phlegm and nasal mucus down into the throat, where muscles in the throat and tongue can prepare to eject it. Once this is done, a U-shape should be formed with the tongue, while simultaneously forcing air and saliva forward with the muscles at the back of the throat. At this point, the phlegm will be in the mouth and is now ready to be spat out as sputum.

Phlegm can exist in different colors. The color could provide important clues about a person's health.