I receive a question regarding this from an email, so I would like to explain this as it offends my literary sensibilities.
Nasal mucus, to give bogies their correct title, is the result of a titanic battle between the bad guys (bacteria and viruses) and the good guys (out wonderful immune system) that goes on almost every day of our lives. We breathe in droplets from other people’s coughs and sneezes, upon which the bad guys are hitching rides, and they settle on the surfaces inside our nose. The nose is amazingly efficient in “sweeping” the air inside it on to the “brushes” that protrude into its passages- so much so that very few droplets and dust particles can pass through it directly into the lungs. When they land on nasal surfaces, our first-line defensive cells produce mucus- a sort of goo- within which there are chemicals that recognize and coat the germs. They are send a chemical message to marshal second-line defensive cells to come to the spot and deal with the invaders. The cells recognize the enemy from their coating of chemicals, and start to engulf them. In the fight, there are casualties on both sides, leaving the mess of dead cells are germs to mopped up by the mucus.
Bogies are this detritus of a battle you probably didn’t know was going on daily inside your nose. Only when it become a terrifying war zone- as in a cold- do you feel the consequences in a sore and itchy nose.