But despite being a little icky, phlegm gets a bad rap.

This germ-fighting goo contains cells and compounds that help us power through a cold, and what turns up in our tissues can be a useful clue about the inner workings of our immune systems.

That's right, it's time for the colorful, chemical secrets of snot.

When we get sick with a cold or sinus infection, our bodies begin to produce more mucus than normal to double down on the viral or bacterial invaders.

At this point, the consistency and color of snot also changes, going from healthy and clear to, well, not so clear.

Think of your snot like a traffic light.

Yellow or white mucus turns up when you're congested, and a higher concentration of living and dead white blood cells have thickened the discharge.

These immune cells might be there to battle a cold, so slow down and take it easy.

If your mucus looks green, that could be due to the presence of a greenish enzyme called myeloperoxidase, which helps produce acids in powerful immune cells called neutrophils.

With neutrophils hard at work, your body is probably in full "go mode," trying to kick a viral infection.

Red mucus means stop picking or blowing… but fear not, small amounts of blood in mucus are totally normal and no cause for concern.

No matter what the color, too much mucus can be annoying or painful - which might bring you to the drug store for relief.

But what you decide to buy should match your symptoms and their root cause.

For example, if you're dealing with a runny nose, one possible culprit is histamine: Histamine plays a pivotal role in allergies and other immune responses by increasing blood flow to snot-producing body tissues.

Fortunately, antihistamine drugs block some histamine from reaching their target mucus-producing cells.

They can also cut down the production of histamine altogether… all of which helps you quit reaching for the tissue box.

Or perhaps you're dealing with an arguably more annoying snot problem - congestion.

If your head is pounding with pressure, decongestants work to reduce blood flow to nasal and sinus tissues that produce mucus, this time by constricting the blood vessels themselves.

Cutting down on the volume of snot and reducing inflammation should help ease pressure on your nose and sinuses.

That could clear things out a little bit easier.

But over reliance on both antihistamines and decongestants can decrease their effectiveness over time, so sometimes, it's best to just rest up and let your immune system do its thing.

But did you know that under the right conditions, some runny noses have nothing to do with being sick or having allergies.

If you suddenly feel sniffly standing out at the bus stop, don't blame it on snot.

That's actually condensation from water in the cold air hitting your warm nostrils.

So you don't have to feel quite so gross about wiping it on your sleeve - yeah, we see you there Kyle.

For more snot science, be sure to check out Anna's video at Gross Science.

She's covering snot 101, what it is, what it does, and everything you could possibly want to know about snot.

Be sure to subscribe to her channel for videos like why dogs eat their own poop, the vomiting defense of birds, and so much more.

While we still have you, be sure to thumbs up and subscribe on your way out, and hey, thanks for watching!