When coughing up mucus, it primarily comes from the mucous membranes lining the respiratory system, which includes the nose, throat, airways, and lungs. Specialized cells called goblet cells and submucosal glands produce the mucus. This mucus is a mixture of water, proteins, and sugars designed to trap dust, microbes, and other foreign particles, protecting the respiratory system. The mucus is typically moved by tiny hair-like structures called cilia, which push it up toward the throat where it can be coughed up or swallowed. When there is inflammation, infection, or irritation in the respiratory tract, mucus production increases, often leading to the cough reflex expelling excess mucus, also called phlegm, from the lungs and airways.
