It’s only been three days since my son’s nose started getting snotty, but that’s long enough to make you wonder why, and how, all this mucus keeps coming out of his nose. At just shy of five-years-old, he’s technically able to handle a tissue himself, but not to the point where he can be expected to be effective in his booger management. Coupled with the sore throat and cough of a nasty cold virus, all this mucus-production feels like a bit of a curse. Of course, it’snot— it’s simply our body’s way of purging pathogens that are trying to take up residence in our respiratory tract.
On any given day, your sinuses are doing double-duty at a minimum. They warm and moisten air before it gets to the sensitive tissue in our lungs, plus captures junk that we don’t really want to be inhaling in the first place. That can be dust, dirt, pollen and of course, viruses and bacteria. Ideally, the layer of mucus that coats the inside of your nose and sinuses is enough to capture these potential irritants, moving the sticky stuff back down your throat with hair-like structures called cilia.
As my son’s clogged nose can attest, sometimes things get through. There’s likely to be some resistance in your mucus from benign bacteria, but your immune system revs up when a pathogen start penetrating cell walls in your nose. Proteins called cytokines are released, which then activate T and B cells that will attack the pathogen directly. To help in that battle, the lining of your nose swells and increases its booger production, hopefully creating enough mucus to grab and flush the offending pathogens out of your body. Unless of course you’re five, in which case you’ll probably get the contaminated snot on your hands and spread it far and wide, infecting everyone around you. (Not that we hold that against you, son!)
From the outside, this all looks like a runny nose. The excess fluid in the swollen mucus lining can lead to gross, drippy discharge in a condition known as rhinorrhea. Sometimes the extra mucus just clogs things up, making us feel horribly congested in the process. You can blow your nose to help with that, but violently trying to force the boogers out of your face can actually damage the cilia that help move mucus around. It can also end up sending pathogens deeper into your sinuses, kicking of new infections. So even though a drippy nose is annoying, it’s actually working as intended.
Of course, sometimes your nose is drippy when it doesn’t need to be. For instance, cold weather can trigger a runny nose in healthy people, albeit for very different reasons than described above. In those cases, the air is probably cold and dry enough to make your mucus linings activate in an effort to keep air properly warmed and moistened on its trip to the lungs. That can lead to extra fluid in your nose that then starts dripping out. Alternatively, there’s a chance that moisture in the air is condensing just inside your nose, forming noticeably large droplets that feel like snot.
Finally, crying can lead to a runny nose because eyes are just filling the place with fluid. As tears drain into your nose, they soften the layer of mucus that’s always present enough to start flowing. That way, your emotional moment can feel a bit sticky too.
My third grader asked: Is the runny nose you get from cold air the reason we call it a ‘cold?’
Basically. A “cold” was first used to describe illness in the 1530s, long before anyone knew to look for the rhinovirus or coronavirus that was actually causing a person’s symptoms. The resulting infection felt enough like the unpleasant effects of being chilled that it easily described what was wrong with someone, even if it did lead to confusion about what actually causes the illness (mostly.)
Source: Why Does Your Nose Run When You’re Sick? by Alexandra Ossola, Popular Science