A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

How does my nose produce so much snot so fast when I have a cold?

October 17, 1997

Dear Cecil:

I'm sitting here with a cold, which means I'm getting that skanky feeling of dehydration when every cubic centimeter of water one consumes is allocated toward snot production. Aside from making me have to cough and blow my nose a lot, it leads me to wonder about the physiology of mucus. Does the body actually use it for something, or is it simply a by-product of some other process? How is it that as soon as I blow it all out, my nose and sinuses seem to fill right back up in less than a second? How does the body produce so much of it so fast? Have any yogis with superior body-wisdom found a way to retain in the body valuable water that might otherwise go to producing worthless snot? Or would that be counterproductive to the healing process?

Cecil replies:

This will pretty much complete our series on the lesser bodily secretions, unless somebody really wants to go into the smegma thing. As is true of all God's creation, mucus is good for you. No doubt you could stand to have a little less of it at times, but this shouldn't decrease our esteem for a fluid that is only trying to defend us against germs, dust, and other foreign matter. Evidently, since you got a cold, this defense against germs wasn't entirely successful. But the mucus is trying. You might show a little appreciation.

Under normal circumstances — that is, when you don't have a cold — nasal mucus is part of the system by which your body conditions "inspired air." (Inspired air is the term doctors use for inhaled air. They could just say "inhaled," but inspired has a much more elegant ring.) The air swirls through your nasal passages and gets warmed up. Meanwhile the dust and whatnot strikes the mucus-lined sides and sticks. Or to put it more technically, it strikes the mucus-lined ciliated epithelium of the posterior nasopharynx and … well, I guess "sticks" is not the word you want to use in this context. Adheres, let's say.  The cilia (little hairs) and mucus then transport the debris to the rear of the mouth, whence you can hawk it up. This is called postnasal drip. Another of life's little annoyances that you ought to be grateful for.

As I say, the above mechanism is not a foolproof antimicrobial defense, and sometimes you get a cold. Your mucus then kicks into overdrive in an attempt to shed the virus or whatever bad thing it is you've got. Sometimes the mucus succeeds, at least to the point where you can continue to breathe through your nose. Sometimes it doesn't and your nose plugs up, and the infection takes root in your sinuses, producing the dreaded green globs and making you sound like your head was whittled from a potato. You think this is better than having a runny nose? I think not. Sorry if I sound like I'm dumping on you, Keith, but I'm trying to put matters in perspective. Your problem isn't the mucus, it's the germs.

The reason you have a seemingly inexhaustible supply of mucus when suffering from a cold is that the mucus-producing cells lining your nasal cavity extract the stuff mostly from your blood, of which needless to say you have a vast supply. The blood transports the raw materials (largely water) from other parts of the body. Fluid from your blood diffuses through the capillary walls and into the cells and moments later winds up in your handkerchief. (This process isn't unique to mucus; blood is the highway for most of your bodily fluids.) Incidentally, you produce less mucus than you may think. One experiment showed that on the peak day of a cold the average person produces about 14 grams of drippings, or roughly half an ounce.

Another question I'm asked from time to time is, what's the chemical formula for snot? (Listen, I've heard worse.) I have no definite answer to this. Ninety-five percent of mucus is H2O, while the remainder is protein, carbohydrate, lipids, and miscellaneous, the proportions and nature of which vary. I found some discussion in the medical literature about what makes mucus, um, stringy, but figured this was something you'd just as soon not know.

Finally, I came across an article entitled "Effects of Drinking … Chicken Soup on Nasal Mucus Velocity." About time somebody researched this. The article says the "Jewish penicillin" (authors' term) is indeed salubrious, although only for half an hour, largely because the healing vapors penetrate the nasal passages and loosen things up. So eat your chicken soup already; mama was right all along.

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