What is a function of mucus

Mucus serves to protect epithelial cells (that line the tubes) in the respiratory, gastrointestinal, urogenital, visual, and auditory systems; the epidermis in amphibians; and the gills in fish, against infectious agents such as fungi, bacteria and viruses.

The major function of mucus is to protect the lung through mucociliary clearance against foreign particles and chemicals entering the lung.