Gross-but-cool fact of the day: Our bodies produce one to 1.5 liters of snot every 24 hours.

If that seems like an awful lot of gooey, gross stuff, consider that mucus does have a purpose: "It's not something that's just random or left over from something else," says William Schaffner, M.D., professor of medicine and infectious diseases at Vanderbilt University School of Medicine.

While you may never be convinced you actually want it, there's a lot you can learn from the mucus you do produce: How much snot is normal? What's up with the different colors? Why does spicy food make your nose run? Here, finally, the answers.

Why We Have Mucus

The purpose of the gooey stuff is to keep your mucus membranes moist. "Moisture is very important because if those cells dry out, as you can imagine, they become somewhat brittle, which creates cracks, which creates little openings in our peripheral defense mechanisms," says Schaffner. This is not only painful but can also result in harmful substances being let into your system. "You can almost think of mucus as a lubricant or a liquid blanket that covers the sensitive mucus membranes."

Mucus also acts as a net, catching unwanted particles and dispelling them back out your nose as snot. "If you're in a dusty environment and you breathe in, the mucus that is in your nose will pick up those dust particles and won't let them get down into your lungs and into your sinuses," says Schaffner.

That also holds true for bacteria. "Everybody's nose has bacteria in it," says Schaffner. "They're kept away from the lungs and our sinuses by our mucus, which, when it comes out, takes the bacteria with it."

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How Much is Normal

We all produce mucus in our mouths, noses, sinuses, throats, lungs, and gastrointestinal tracts. But you'll likely only notice a dollop of the wet stuff each day. "Normally we [notice] less than a teaspoonful a day, most of which is swallowed or evaporates," says Neil Schachter, M.D., professor of medicine at Mount Sinai Hospital. "Cold weather increases the amount of liquid produced in the nasal passages."

And everyone's body produces mucus at different rates, depending on their height, weight, and immune system, says Schaffner. You're the best person to know how much "snot" is normal for your own body.

Some people also experience gustatory rhinitis, or nasal inflammation caused by ingesting certain foods. "For example, some people, if they eat spicy foods, all of a sudden their noses start to run," says Schaffner. "That's a curious kind of reflex. Some people get that same affect when they drink milk." It's unclear why this happens—chalk it up to one of life's little mysteries.

When Mucus Changes Color and Consistency

"Healthy mucus is usually clear and thin," says Schachter. "When it becomes thick and cloudy, it's a sign of inflammation, infection, or allergy. It becomes yellow or green as the result of white blood cells dying in response to irritation."

In plain English: Our bodies send white blood cells to our noses to fight viral infections—and it's those white blood cells that turn our mucus yellow or green. (Unfortunately, antibiotics don't treat viral infections—you just have to keep blowing your nose until the infection has run its course, and you'll know when that happens because your snot has returned to its clear, more liquid form.) You can also handle excess mucus with a saline rinse, says Schachter; it loosens crusty bits and relieves congestion.

And just like different bodies produce different amounts of mucus, we all have different normal snot consistencies. Yours may change seasonally if you're affected by allergies, which you can treat with an antihistamine.

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When Snot is a Cause for Concern

If you see blood, call your healthcare provider immediately. "[That means] the inflammation has eroded through the mucus membrane and into little blood vessels, and you may need someone's attention to get that stopped," says Schaffner.

Otherwise, if your mucus has traveled into your chest—and worse, you're coughing up yellow-tinged sputum—you should also call your doctor. You could be experiencing pneumonia or bronchitis—but an M.D. can tell you exactly what's up.

By itself, Schaffner says, mucus is rarely a sign that something is wrong; it's the accompanying symptoms—muscle aches, severe coughing, lethargy, or blood—that should catch your attention.

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Jillian Kramer Jillian Kramer is a freelance journalist whose work has published in Food & Wine, Travel + Leisure, Martha Stewart Living, SELF, and more.

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