Where Does Snot Come From? | By Sydney Rudko

In case you don’t follow me on twitter, and are not privy to the happenings of my life (most notably what I ate for dinner, and name suggestions for the Kimye baby), you should know that I am sick with a cold. Today while I was sitting on campus sneezing my heart out to a friend, he asked me where all of the snot comes from when we get sick. While at the time I rolled my eyes at him, I now see this as an extremely valid question. Where does all that snot come from?

We put a lot of weird stuff in our mouths. No, really. Think about the last time you went for a jog. You’re mouth wide open, gasping for air, wondering if this time you’ll make it to the end of the driveway before collapsing. But alas, your step falters as you run past your Corolla, and you fall onto the pavement unleashing a torrent of dust and debris into your already rasping nasal passages. Think about all the dirt, and grime, and feces, and bugs you inhaled! Even better! Remember last week when you read that funny Facebook status in the bathroom? Yeah, you know what you inadvertently inhaled, but don’t worry about it because your body is well equipped to handle these foreign invaders. It is armed and ready in your mouth, eyes, ears, and even in your personal places to defend you ‘till the end.

Your mouth, nose, and airways are lined with special cells whose job is to secrete mucus, even when your body isn’t under attack. It seems gross, but mucus is a great way to trap a lot of incoming debris and bugs from penetrating further into your body. The bugs get trapped in the mucus, and are removed from the body when you blow your nose or cough. This is a pretty effective system for dealing with just about everything you encounter on a daily basis, but at some point a smarmy virus or bacteria is going to breach this barrier and try to colonize your insides. When this happens, the rest of your immune system is recruited to the area of infection and begins producing specialized molecules called chemokines. Chemokines are how immune cells talk to one another and coordinate an attack. These are actually very interesting and important molecules. After all you wouldn’t want cells equipped for killing bacteria trying to handle a viral infection. Some of these chemokines will stimulate your mucus secreting cells to produce even more snot so you can remove the replicating bugs from your body. Furthermore, during an immune response a lot of damage is inflicted on your own cells. Excess mucus is a great way for the body to flush away some of your own cells that have been killed or damaged in the infection process.

This brings me to probably the coolest snot question ever. What makes your snot funny colors? Normal healthy snot is clear or milky white colored, but when you’re sick it might be green or yellow! This is actually due to your immune system. When you’re sick, your immune system recruits a special cell called a neutrophil. Neutrophils kill pathogens by secreting a plethora of antimicrobials to kill the invaders. These bug-fighting compounds are stored inside their cell bodies. Near the end of an infection your neutrophils begin to die off, and as they do they often leak some of those compounds into your mucus. One of these toxins is called myeloperoxidase and when it is released into your mucus it turns it a yellow-green color. The color is produced by iron, a cofactor that is required for the enzymes. It is the oxidation state of the iron that produces the color!

So while you’re feeling under the weather, remember that you aren’t sick, you’re simply experiencing the wonders of biology first hand.

Image courtesy of Svenstorm on Flickr.

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