=Main reasons for phlegm
Viral infections: When you have a cold, fever, or flu, the body produces more phlegm.
Bacterial infections: Lung infections (Bronchitis, Pneumonia) can cause thick, discolored phlegm.
Allergies: Allergies to dust, smoke, pollen, and pet dander cause swelling in the airways and increase phlegm production.
Asthma: In people with asthma, the airways become inflamed and excess phlegm is produced, causing shortness of breath.
Smoking: Smoking damages the cells in the lungs and causes chronic phlegm (Chronic Bronchitis).
Environmental pollution: Air pollution irritates the lungs and causes phlegm to form as a defense.
Dry weather: When the humidity in the air decreases, the lining of the lungs dries out and the body has to produce more mucus.
