What is phlegm?

Phlegm is a sticky, gel-like fluid secreted by the mucous membranes in the respiratory tract of humans and mammals in general. It is mainly made up of lipids, glycoproteins and immunoglobins, as well as other substances. Its function is generally to trap foreign agents that could enter the body through the respiratory tract. Excessive phlegm occurs as a sign that the body is fighting some kind of infection. The composition and color of phlegm can vary greatly, from watery to thick or clear to brownish, depending on the environment and the state of the body's immune system at any given time.

Working not only to lubricate the airways and nasal passages, phlegm can also trap dust, allergens, viruses, and bacteria that enter the body from outside. These foreign bodies get trapped and neutralized by mucus and are then expelled from the body by coughing or sneezing. That's why while cough suppressants can provide relief, they can also suppress the immune system's necessary removal of waste.

The color of the mucus that is coughed up is usually an indicator of what type of infection a person has. The normal mucus of a healthy body is typically, but not always, light in color and generally thin in composition. An irritation of the nasal passage, such as from allergies or asthma, can cause thicker, whiter mucus. White or clear phlegm may still be present during the initial stage of the flu, but it will still be infectious during that time. Constant coughing up white or clear mucus could indicate a mild viral infection, most of which heal on their own within five to seven days.

Yellow or greenish-yellow phlegm usually indicates an active infection. During this time, the mucus will consist more of dead white blood cells and dead bacteria or viruses. This is because the dead cells that had been fighting the infection are shed from the body through the phlegm, resulting in a yellowish color.

Green mucus still indicates an infection, but increasingly dormant. The green color is essentially caused by active, yellow phlegm that has stagnated and turned green. More rarely, coughing up green mucus can be a symptom of cystic fibrosis.

Red mucus, or redness in the otherwise healthy-looking interior, is usually a sign of bleeding. This may have a benign cause, such as a nosebleed or a cut on the nose from scratching or rubbing. A high concentration of blood in the mucus, or small spots or streaks of blood over a long period of time, may indicate something more serious, such as bleeding in the lungs, bronchitis, or pneumonia. Coughing up blood can be a symptom of a major internal injury or illness, such as tuberculosis, and should be checked with a doctor as soon as possible.

Brown mucus is usually caused by old, stagnant blood. Smokers can also have brown mucus, and many often expel it in response to chronic bronchial inflammation caused by smoking. A smoker's mucus will typically, if examined, be grainy in texture. This is because cigarettes that normally trap foreign bodies like dust and dirt have been damaged by smoking. Increasingly brownish mucus in a smoker may indicate underlying respiratory problems.

Pink mucus can sometimes be an indication of asthma due to a specific type of white blood cells present during the condition. However, foamy pink mucus is a classic sign of pulmonary edema, a serious condition that, if left untreated, could lead to coma or death. Foam in mucus usually comes from a buildup of fluid in the lungs. Any case of foamy mucus should be checked with a doctor as soon as possible.

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