Why is snot yellow? And where does it come from?
September 20, 2011 12:41 PM   Subscribe

Why is snot yellow? And where does it come from?

I've contracted a virus about 10 days ago. About 8 days ago I suffered from a runny nose, and then 7 days ago things progressed into a massive sinus headache (all of my teeth hurt), and chest congestion - a deep whooping cough.

I've been coughing up phlegm, but not a lot, and I don't have a chest infection.

The cold is getting better (I can do errands and go for a walk without feeling fatigued), but I still get masses of yellow snot every once in a while.

I know it's normal, but what biological process is causing this?

I can breathe fine through my nose, but suddenly I'll feel a bit of a clog at the back of my throat. I'll blow my nose and there will be this big lump of gummy, yellow snot.

I'll keep blowing and blowing, and more snot will come out... from somewhere.

This tends to happen every 20 minutes.

Is the yellow snot hiding out someplace? Is my body producing it on the fly? It's just that it's an amazing volume, and it keeps coming out.

Why is the snot yellow? Why is green snot green (I don't have green snot)?
posted by KokuRyu to Health & Fitness (7 answers total) 7 users marked this as a favorite
Snot, previously. (eeew)
posted by jquinby at 12:43 PM on September 20, 2011

My snot is only yellow-yellow when it's pollen season. My snot is occasionally gray (like, every time I blew my nose when I was in London (pollution, I'm assuming) and that time I had to clean off a really old skeleton that had been hanging in a closet in the anatomy lab for years (probably should have worn a mask). My snot has been cloudy and off-white (maybe this is what you're referring to as yellow?) when I've been mildly sick. My snot has only been green when I have been really, really sick (like, requiring an antibiotic sick). The color is just from a buildup of the bacteria that are causing the infection, which are usually colored themselves.

I suggest using a neti pot if you don't already. It does a really good job of flushing the snot and boogers out. It's a must for me during allergy season if I want to breathe.
posted by phunniemee at 1:53 PM on September 20, 2011

Best answer: Well, let me look at my anatomy book. [I'm literally summarizing from an anatomy book here.]

The part of your nasal cavity just above your nostrils is called the nasal vestibule. It's lined with skin have sweat glands, oil-producing glands, and hairs, which are meant to filter out dust and pollen and such. The rest of the nasal cavity, farther up, is lined with two types of mucous membranes. Some of it is olfactory epithelium, which contains smell receptors. The rest of it lined with respiratory mucosa.

Snot comes from respiratory mucosa. Think of this as a super-specialized kind of skin. Rather than having flat, dead, keratinized (waterproofed with protein) cells on top, like the skin of your arm does, it's got ciliated cells intermixed with goblet cells. Let's unpack those one at a time. Cilia, as you may remember from high school biology, are little armlike projections on the surface of the cell that help move stuff along their surface. Goblet cells are, as the name suggests, cup-shaped cells that produce and exude mucus. There are also scattered serous glands. Serous fluid is a watery fluid that contains enzymes. In the case of your nose, the enzyme is an antibacterial enzyme called lysozyme.

The lysozyme attacks bacteria as it enters your nose, while the sticky mucus produced by your nose physically traps dust, etc that got through those hairs in your nasal vestibule.

But check this out, yo! Your body normally produces about a liter of mucus a day. When you're healthy. But on most days, you don't even blow your nose, so, wtf? Yeah, that's when we get back to the cilia. Those little cell projections crate a current that moves the mucus back toward your throat, where it's normally swallowed (and destroyed by your stomach acids). Contaminated mucus, taken care of by your body's natural defenses, and you don't even notice.

When it's cold outside, these cilia don't work as well, and the current of disgusting, contaminated mucus doesn't move as fast, so it can build up in your nose and start to drip out the other way. That's why on a cold day, your nose might get stuffy even if you're not actually sick.

Now, in your case, you are actually sick. This means that your respiratory muscosa is inflamed and working double-time. It's producing A LOT of mucus. Thick mucus. (This is one of the reason that people always tell you to drink water when you have a cold; being well-hydrated means that your body can produce more serous fluid and thin that gross stuff out.) Plus, your body has sent neutrophils (a kind of white blood cell) to try to stop the pathogens invading your nose. It's a chemical companion to these cells that produce a lot of the color we notice in our nasal mucus, but that's better explained here. (Skip to "Why is snot green?")
posted by purpleclover at 1:58 PM on September 20, 2011 [46 favorites]

Response by poster: That answers my question. Thank you!
posted by KokuRyu at 2:17 PM on September 20, 2011

It's lined with skin that havehas sweat glands,...

The rest of it is lined with respiratory mucosa.

It's a chemical companion to these cells that produces

Gah, some day I will write a long answer that isn't riddled with typos, but today is not that day.
posted by purpleclover at 2:44 PM on September 20, 2011

Response by poster: On the plus side, the bit you excerpted here sounds like a They Might Be Giants song
posted by KokuRyu at 7:50 PM on September 20, 2011

I am on the back side of a cold, and this helps explain the socially-unacceptable symptoms I am experienceing today, despite feeling better. :7) Thank you for this.

One question, though: does the extra mucus production indicating an on-going illness also imply ongoing contagiousness, or can I be super-gross without also risking the good health of those around me?
posted by wenestvedt at 8:34 AM on September 21, 2011

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