Mucus is a slick substance secreted by the mucous membranes that line many of the body’s inner surfaces, such as the lungs and the nasal passages. It consists of proteins, antimicrobial enzymes, antibodies, and salt. While the average person produces around 4.25 cups (approximately 1 liter) of the secretion each day, it is normally fairly thin and unnoticeable. It is usually only when the body becomes infected that it takes on the nostril-plugging, cough-rousing consistency that sends many running to a healthcare professional for relief.
This substance has three primary functions: keeping bodily tissues moist, trapping foreign bodies to prevent infection, and attacking the causes of existing infections. Its moisturizing properties are important to the health and comfort of the body’s many mucous membranes. Once secreted, it forms a kind of shield of dampness over these surfaces, without which the membranes would quickly become dried out and irritated.
While the stickiness of mucus may be disagreeable, it is this very property that allows the substance to perform an important protective duty. It traps foreign bodies like bacteria in its gooey clutches before they can set up shop in the body and cause an infection. Once these bodies have been trapped, they are eliminated by the antimicrobial enzymes contained within the substance.
Despite the body’s best efforts to nip infection in the bud, sometimes viruses and bacteria manage to invade and cause illness. When this happens, the mucus plays yet another role. Its antibodies seek out the infecting bodies and then kill them.
It is when the body has been infected that the mucus takes on the qualities with which it is generally associated: green color, thick consistency, and seemingly endless abundance. This green hue is caused by a green enzyme contained in the antibodies. When the body is infected, these antibodies are dispatched to in larger quantities than usual, giving the substance a noticeable coloration.
Thickness and increased production are also defensive features that enhance the material's ability to trap and neutralize infection. While in the throes of a drippy cold or stuffy sinus infection, it can be tempting to sideline respiratory secretions with a decongestant or antihistamine. Before cursing the sticky stuff, however, patients should remember that it plays an important role in making — and keeping — the body healthy.