Phlegm is a specific type of mucus that originates in the lungs and throat. It is produced by the lower airways in response to inflammation. Coughing up phlegm is a normal symptom of colds and other health conditions, but coughing up phlegm without feeling sick could indicate a more serious underlying issue like heart or lung disease. There are several health conditions, ranging from mild to severe, that can result in coughing up phlegm, including lung diseases such as chronic bronchitis, pneumonia, cystic fibrosis, and COPD (chronic obstructive pulmonary disease). Certain environmental and lifestyle factors can also contribute to coughing up phlegm, such as a dry indoor environment, low consumption of water and other fluids, high consumption of fluids that can lead to fluid loss, such as coffee, tea, and alcohol, and smoking.
In summary, phlegm is caused by inflammation and irritation in the respiratory system, and can be a symptom of various health conditions or environmental and lifestyle factors.
