Phleg

Phleg is a term that historically referred to a thick, watery fluid produced in the respiratory tract. In ancient Greek medicine, it was considered one of the four humors, imbalances of which were believed to cause illness. The concept of phlegm as a humor has been superseded by modern medical understanding of physiology and pathology.

In contemporary usage, phlegm is often used interchangeably with mucus, particularly when it is expelled from the respiratory system, such as during coughing. Mucus is a gel-like substance produced by mucous membranes throughout the body, including the lining of the nose, throat, and lungs. Its primary functions are to lubricate, protect, and trap foreign particles.

When the respiratory system is irritated or infected, such as by a cold, flu, or allergies, the production of mucus can increase. This excess mucus, often thicker and sometimes discolored, is what is commonly referred to as phlegm. It can accumulate in the airways and be expelled through coughing as a protective mechanism to clear irritants and pathogens. The color and consistency of phlegm can sometimes provide clues about the underlying condition, though medical diagnosis relies on a comprehensive evaluation.