(Medical News Today) — Phlegm is a type of mucus that is produced in the lungs and nearby lower respiratory tract airways. This kind of mucus has a crucial role in preventing germs and materials from entering the airways and lungs and potentially causing an infection.

Other areas of the body, including the upper respiratory tract (nose, mouth, and throat) and gastrointestinal tract (gut) also secrete mucus.

Typically, mucus is clear and thin and not noticeable at all. When someone gets sick with a cold or an infection, the mucus can become thickened and change colour.

In this article, we take a look at the various colours that mucus or phlegm can be, and what these mean for a person’s health. We also examine different textures of phlegm and explain what a person can do if their phlegm changes.