We don’t usually spend much time thinking about our snot—until it starts coming out of our noses. Then we blow it, and wipe it, and, yes, look at it, all the while trying to figure out what’s really going on. Some of us have definitely spent more time than we’d like to admit analyzing the contents of our tissues.

Normal snot—or as the pros call it, nasal mucous—is clear, watery, and totally under the radar.

“Our body produces about 1 liter of mucous and saliva a day but we don’t notice the normal production,” Erich P. Voigt, M.D., associate professor in the department of otolaryngology at NYU Langone Medical Center, tells SELF.

In fact, Voigt says we take our nasal mucous for granted. “It’s actually a really important part of our body,” and without it, we’d get sick very often. “It’s a protector of our airways,” he said “Everything we breathe in gets filtered by that mucous.”

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It’s filled with infection-fighting antibodies, which kill off pathogens we inhale before they have the chance to make us ill. Nasal mucous also moisturizes the air we breathe and regulates its temperature so it’s just right before entering our lungs.

But when nasal mucous is abnormal, it can tell you a lot about your health. Here’s what your snot’s color and consistency can reveal.

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If your snot is clear and runny…

This is a classic symptom of seasonal allergies. 

“If it’s the start of spring and all of a sudden your nose gets stuffy and starts running and it’s clear,” it’s likely you’re having an allergic reaction, Voigt said.

This will typically be paired with an itchy nose and sneezing. 

Clear, runny snot can also be a sign of an upper respiratory virus. If it’s paired with a fever, or you’re just feeling a little blah, and it lasts for three or four days, chances are you have a viral infection. The best example: a brief cold.

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If your snot is clear and thick…

Clear, thick nasal mucous (the kind that clogs up your nose and doesn’t seem to budge no matter how much you blow) may signal a chronic allergy, like if you’re allergic to dust.

“It’s everywhere year round, so you won’t feel that runniness anymore, you’ll just feel stuffy all the time and the nasal mucous might be thicker and more plentiful than usual,” Voigt said.

Dehydration can also make mucous thicker.

“People who think they have too much mucous many times are, in fact, not making enough so it’s too dry and not flowing nicely,” Voigt explains.

If your snot is bloody…

A few specks of blood in your snot is actually pretty normal, especially in the winter when heating systems make the air inside super dry. When the membranes lining the inside of the nose get dried out, crusts and cracks can form and bleed a little bit. But if there’s a lot of blood in your snot frequently, or you get full-on nosebleeds on the reg, see a doctor to rule out any bigger medical conditions.

“It could be tumors in the nose or sinuses, but they’re rare,” Voigt said.

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If your snot is green or yellow…

Any time your snot changes color, it means you have some sort of infection. How long the discoloration persists is also key in determining what type of infection you have.

“If it’s temporary and peaks in three to four days and gets better on its own, that can be due to a viral infection,” Voigt explained.

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Nasal mucous is typically clear and runny in a cold’s initial stages, but if the virus persists for longer it can turn snot yellow or green after a few days. Other viral infections, which should also clear up within a few days, can cause a change in snot color, too.

If this abnormal coloring persists for longer than a week—maybe even turning orange or brown—then it’s more likely to be a bacterial infection, like a sinus infection. This is when your doc will typically need to prescribe antibiotics to get you healthy again.

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If your snot is sticky, stinky, and discolored…

Some people suffer from chronic sinusitis, which makes nasal mucous very thick and glue-like, Voigt describes, discolored (green or yellow), and even odorous. A chronic infection one can last for weeks or months at a time, causing serious congestion, difficulty breathing, pain and swelling around the sinuses, and a bad cough. Not fun. If you have abnormal nasal mucous that just won’t clear up with time or antibiotics, visit a specialist like an otolaryngologist (a ear, nose, and throat doctor) to figure out what’s causing your symptoms.