No matter how hard humans try to be civilized, there is no getting around the fact that some aspects of our body, and how it works, are frankly...disgusting. The normal flora bacteria that colonize and protect your body also generate body odor and flatulence. Our mucous membranes produce loads of slimy mucus, and those of your nasal cavity occasionally generate sticky little boogers.
* What Are Boogers Made Of? *
The membranes that line the openings of your body (nasal cavity, GI tract and urogential area) are called mucous membranes. These membranes are made of living cells that secrete a sticky substance called mucus (myoo-kus).
Mucus is composed mostly of water, mucin and enzymes, like lysozyme, which helps break down invading materials and protect you. Mucin is a big organic molecule made of both sugar and protein, and it becomes very sticky when mixed with water.
* Why Do We Make Boogers? *
Your sinuses make a whole lot of mucus, and, although you might find your snotty nose to be an inconvenience, this sticky materials has an important job; it protects the delicate tissue of your lungs.
The hairs in your nose and the sticky mucus trap many of the tiny particles that you inhale (such as dirt, dust, pollen and germs), and prevent them from getting into your lungs where they could cause irritation and possibly infection. Mucous is kind of like fly paper for keeping your lungs clean.
Sometimes the mucus, with its trapped dirt and debris, clumps together and dries out a bit from all of the air constantly moving past. These mucous blobs can become even stickier as they dry, creating sticky boogers. Sometimes these blobs completely dry out and you are left with crispy boogers.
* Getting Rid of Your Boogers *
The cilia (short hair-like projections) on the cells of the mucous membrane move the mucus to the front of the nose and back of the throat to be eliminated from the nasal cavity, to be replaced by a constant supply of fresh debris-trapping mucus.
When you want to clear the snot and crusties out of your nose, but be sure to blow (not pick). Picking your nose, besides being a nasty habit, introduces the microbes on your hands into your nose where some of them can set up house and cause disease.
* Sources *
Bauman, R. (2004) Microbiology. Pearson Benjamin Cummings.