"Mucus is produced by submucosal cells as well as goblet cells in the respiratory system. It consists of mucin, a highly glycolsilated peptide. Upon stimulation, MARPKs (myrastine-alanine rich protein kinases) signal the binding of mucin filled vesicles to the plasma membrane. The fusion of the vesicles causes the release of the mucin, which as it exchanges Ca2+ for Na+ expands up to 600 fold. The result is a viscoelastic product of interwoven molecules called mucus." -Source: http://en.wikipedia.org/wiki/Mucus

To better understand snot and boogers, lets start with mucus. Mucus is thick, sticky, slimy and a good thing. Mucus is so important that it’s found all over nature. Inside your nose, it’s a thick, sticky, wet pudding-like gunk that coats your skin and hairs. Mucus is made by, mucus membranes. Your body has mucus membranes in all sorts of places: the stomach, intestines, nose, lungs, eyes, mouth, and the urinary tract all contain mucus membranes that secrete mucus. For now, we will "pick the nasal membranes and mucus" as our topic of interest. Mucus becomes very important with every breath that you take. Each time that you take a breath, there are three very important things that happen. 1. The air that you breathe in is cleaned by tiny hairs in your nose, trapping little bits of dirt and dust and germs that come in through your nose. 2. As you breathe, the air is made slightly wet. Your nose having damp passages does this. 3. The next thing that takes place when air enters your nose is that the air is warmed. This happens because the blood flows through the lining of the nose and gives off heat. Even though these three actions are to keep you healthy, germs can sometimes get into your respiratory system. The germs start growing in your nose, throat and lungs. You have a cold! When you have a cold the linings of your nose and / or throat swell. Thick, clear liquid called mucus forms and its purpose is to wash away the germs. The mucus builds up and blocks the air passages. This is what causes a stuffy nose and a cough. "Snot", is just another word for mucus. Snot is beautiful human slime. When bits of stuff get stuck in your nose hairs, it’s the mucus or snot that surrounds the stuff and traps it. Boogers are dried-up snot and dirty nose debris. They can be small, slimy lumps or big, dry, brown clumps. Either way, boogers are filled with the junk that’s in the air you breathe. Dust, pollen, germs, sand, fungi, smoke, small particles from outer space! The good thing about your mucus is that it helps trap all this junk and keep it from getting close into your lungs. It seems like the main function of mucus, snot, boogers, whatever you want to call it is to trap particles, junk in the air inhaled through the nose and keep our lungs clean. Exhaling through the nose helps to expel, to push out the mucus with the trapped dirt in it. Our nose really acts like a vacuum cleaner for the air, and blowing our nose is like emptying the bag. http://www.wsu.edu/DrUniverse/snot.html http://www.coolquiz.com/trivia/explain/docs/booger.asp http://www.kidzworld.com/article/3267-bone-up-on-boogers