What Are the Causes of Mucus in the Lungs?
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Mucus, a slippery and sticky fluid found throughout the body, plays an important role in the health of the respiratory system. Lung and airway mucus traps dust, bacteria, viruses and other airborne particles, then gets slowly propelled towards the throat by the cilia -- the tiny hairs that line the airways. While the respiratory tract depends on mucus to protect and lubricate the airways and lungs, excess mucus production is not normal, and can be caused by exposure to irritants, pollutants or other infection or allergy-causing substances. Excess mucus can also be a symptom or a consequence of certain health conditions. If you have too much mucus in your lungs, see your doctor to determine the cause and understand your treatment plan.

Allergens, Infectious Agents and Pollutants

Although the presence of mucus in the respiratory tract is expected, having a wet cough or chest congestion is a sign of too much mucus, or phlegm. When mucus is excessive or thick, the cilia that line the respiratory tract can become overworked, prompting the cough reflex to help clear the excess. Overproduction of mucus can be caused by allergens, which are substances that causes allergic reactions -- such as dust mites, pollen or mold. Also, the body’s response to viruses or bacteria boosts mucus production as the body tries to fight the infection. Air pollutants such as smoke, mold, car exhaust or certain chemicals can also trigger phlegm buildup.


The lungs of smokers are exposed to twice the levels of airborne particles compared to nonsmokers, according a review published in the September 2007 issue of “Respiratory Care.” Thus, more mucus is produced in the respiratory system of smokers, as the lungs and airways work overtime trying to clear these pollutants. In addition, smoking can damage the cilia, causing mucus accumulation and the characteristic smokers cough. Constant coughing and long-term smoking can also cause damage to the airways, which directly cause the body to increase mucus production, according to a June 2003 review in “Nursing Times.”Pneumonia

Lung Disease

Lung diseases can lead to abundant and thick mucus production, making it difficult for the cilia to clear excess from the lungs. Several short-term and ongoing lung diseases are known to increase mucus, including chronic obstructive pulmonary disease (COPD), a term that refers to a group of lung diseases which impair the flow of air in and out of the lungs and make it difficult to breathe. Emphysema and bronchitis are a few of these conditions categorized as COPD. An article in the September 2006 issue of “Canadian Respiratory Journal” reported that the abnormal secretion of mucus in these conditions is triggered by a variety of factors, including inflammation, bacteria and the body's immune response. Another serious illness linked to mucus is cystic fibrosis, an inherited condition characterized by abnormally thick and sticky mucus that builds up in the lungs.


If you have signs of excess mucus in your lungs, such as a persistent, wet cough, or if you have a fever, wheezing or a cough that lasts more than 2 weeks, see your doctor. Also inform your doctor if you have unexpected weight loss or other chest discomfort that won’t go away. If you are coughing up blood, seek immediate medical attention.

Reviewed by Kay Peck, MPH RD