Coughing up phlegm, also known as mucus or sputum, is the result of many conditions affecting the lungs. After the nose or mouth, air is inhaled into the trachea, or windpipe, which extends from the back of the throat through the neck and into the chest. There it divides into 2 tubes -- one to each lung. The tubes then divide again and again to different segments of the lungs. These tubes have special glands in them that make mucus to help trap debris. Some short-term or long-term conditions cause these glands to multiply or be more active and produce more mucus.
Infection and Allergies
Respiratory infections and allergies can cause excess mucus production, partially blocking your airway. As you sleep, excess mucus develops, and may travel from your nasal passages into your throat. In the morning, you may cough up phlegm as your body attempts to clear your airway.
Asthma causes the airways and lungs to have an exaggerated response to noxious environmental factors, including cold air. The tubes of the lungs quickly constrict, and large amounts of mucus can be produced. This results in difficulty moving air. Some types of asthma are more predominant at night.
Chronic Obstructive Pulmonary Disease
Chronic obstructive pulmonary disease, or COPD, is a lung disease that includes both emphysema and bronchitis. Emphysema is the destruction of normal lung tissue, leaving empty spaces in the lungs where functional lung tissue used to be. The result is less tissue to take oxygen into the blood. Bronchitis is long-term overgrowth of the glands that make mucus in the tubes of the lungs as well as a narrowing of airways. COPD may cause you to cough up phlegm in the morning.
Congestive Heart Failure
Heart conditions such as congestive heart failure can cause a wet cough in the morning. The heart has trouble moving a higher than usual blood volume through the body, causing fluid build-up. This fluid accumulates in the lungs, particularly at night when a person is lying flat. This can lead to shortness of breath and a wet cough at night or in the morning.