Mucus is produced by secretory specializations called Bowman's glands that are distributed throughout the olfactory epithelium. When the mucus layer thickens, as during a cold, olfactory acuity decreases significantly. Two other cells, basal cells and sustentacular (supporting) cells, are also present in the olfactory epithelium.
— Neuronscience 6th Edition
by Dale Purves, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, Richard D. Mooney, Michael L. Platt, Leonard E. White