Phlegm is a thick, sticky substance produced by the mucous membranes in the respiratory system. It plays a crucial role in trapping dust, bacteria, and other particles, helping to keep the airways clear. When a person has a cold or allergies, the body may produce more phlegm to help fight off infections or irritants. Phlegm can vary in color and consistency, which can indicate different health conditions. For example, clear phlegm is usually normal, while yellow or green phlegm may suggest an infection. Excessive phlegm can lead to coughing and discomfort, prompting individuals to seek relief through remedies or medications.