Phlegm

Phlegm with a Canadian quarter for scale.

Phlegm (pronounced /flεm/) is sticky fluid secreted by the mucous 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 of glycoproteins, immunoglobulins, lipids, etc.

In ancient (and now entirely discredited) Hippocratic medicine phlegm was counted as one of the four bodily humours, possessing the properties of coldness and wetness, and responsible for apathetic and sluggish behaviour. This old belief is preserved in the word phlegmatic.

Colors of phlegm

Phlegm may be of several different colors.

• "Healthy" phlegm is normally clear or white; however, the initial state of the common flu when the phlegm is still clear can also be the most infectious period.
• Yellow phlegm means that the immune system is responding. It is commonly taken to be a sign of bacterial infection and physicians often prescribe antibiotics as a result. When the cause is a viral infection such as influenza or the common cold, this treatment is thought to be incorrect. The development of antibiotic resistance may result from such overprescription.
• Greenish or brownish phlegm is nearly always a sign of infection. Greenish or rusty phlegm or phlegm with rusty spots can also be a sign of pneumonia and/or internal micro-bleedings.
• Coughing up brown phlegm is usual for those who smoke. This is due to resin sticking to the viscous texture of the phlegm and being ejected by the body.
• Another type of phlegm often associated with smoking is brownish gray in color. This variant is encased in clear saliva. When spread out, the brown-gray "core" is shown to be grainy in composition, as opposed to holding together. This is simply dust and other foreign matter and may be caused by damage to the cilia, as in COPD patients.

Illnesses related to phlegm

Phlegm may be a carrier of larvae of intestinal parasites (see hookworm). Bloody sputum can be a symptom of serious disease (such as tuberculosis and lung cancer), but can also be a relatively benign symptom of a minor disease (such as bronchitis). In the latter case, the sputum is normally lightly streaked with blood. Coughing up any significant quantity of blood is always a serious medical condition, and any person who experiences this should seek medical attention.

Phlegm and humourism

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 is closely related to the ancient theory of the four elements and states that all diseases and disabilities result from an excess or deficit in black bile, bile, phlegm, and blood. Hippocrates, an ancient Greek thinker, is credited for this theory, about 400 BC. It influenced medical thinking for more than 2,000 years, until finally discredited in the 1800s.

Other concepts

Phlegm was thought to be associated with apathetic behavior; this old belief is preserved in the word phlegmatic."

Sir William Osler’s 1889 Aequanimitas discusses the imperturbability or calmness in a storm required of physicians. "Imperturbability means coolness and presence of mind under all circumstances, calmness amid storm, clearness of judgment in moments of grave peril, immobility, impassiveness, or, to use an old and expressive word, phlegm." This was his farewell speech at the University of Pennsylvania in 1889 before becoming Physician-in-Chief at the recently founded Johns Hopkins Hospital in Baltimore, Maryland. This is from "Celebrating the Contributions of William Osler" in the Alan Mason Chesney Medical Archives of the Johns Hopkins Medical Institutions."