Mucus

Viscous, slippery, glycoprotein-rich secretion produced by mucous membranes and specialized epithelial cells, serving to lubricate, hydrate, and protect underlying tissues, entrap particulates and pathogens, and participate in local immune defense along respiratory, gastrointestinal, genitourinary, and other mucosal surfaces. Possible causes for excess mucus production are infections (common cold, flu, bronchitis, sinusitis), allergies, irritants, chronic disease (asthma, COPD, cystic fibrosis), and acid reflux.