The causes of phlegm can be diverse, yet at the same time these causes can remain quite closely related to each other. Phlegm, which is a type of mucus contained in the respiratory passages, can be caused by smoking and allergies, cancer or bronchitis. It is very likely that the most common cause is related to the common cold, and most people can recover from phlegm symptoms, such as coughing up mucus, by letting the cold run its course. As always, it is best to speak to a doctor to determine the exact causes of phlegm, as it can be due to severe conditions in a small number of people.
Phlegm is a form of mucus secreted through the respiratory passageways, which the body starts to clear by coughing and sneezing. Coughing and sneezing are symptoms and not causes of phlegm, and are only the body's mechanisms of maintaining health and balance, or what is commonly known as homeostasis. Usually the causes of phlegm are the result of a cold or infection that affects the respiratory system and causes large amounts of mucus to be produced. When colds or illnesses are the causes of phlegm and mucus, it is usually treated with topical creams and decongestants to break up the phlegm in the airways.
Smoking is also a common cause of phlegm, and most normal smokers develop coughing and the buildup of mucus in their airways over time. Sometimes this can become quite severe, as continuous coughing can escalate into an episode that induces respiratory failure and then death. Stopping smoking can reverse phlegm, and not smoking can prevent the buildup of mucus later on. Often, heavy cases of phlegm buildup due to smoking can be treated by prescription decongestants, although it is sometimes recommended to allow the condition to clear up on its own.
Other causes of phlegm may include allergies, as the buildup of mucus can be caused by an allergic response to any outside factor. Most allergens that promote phlegm include pollen and plant allergies, however, food and animal fur allergens can also cause phlegm. The best treatments for these conditions include avoiding the allergen or taking prescription medications designed to fight the allergic response. Sometimes phlegm can also be caused by nasal cancer, making it important to see a doctor if chronic mucus occurs and is maintained over time.