Feeling sniffly, but not sure if you’re coming down with a bug? Take a cue from your used Kleenex. As the American Chemical Society's latest Reactions video explains, the color and consistency of snot can serve as a barometer of your health.

Our noses and sinuses always produce mucus, which keeps both the nose and throat moist and humidifies the dry air we breathe. Normally, mucus moves from the sinuses to the nose and then into the throat, at which point we swallow it (without really noticing). But when we’re ill, we generate extra mucus to fight the viral infection as part of our inflammatory response.

Not only do our bodies make more mucus when we’re sick, we'll notice that our snot looks different, too. Normally, it's clear and watery. But when we’re congested, it thickens and turns yellow or white, thanks to a high concentration of living and dead white blood cells that may have been deployed to fight a cold. If your mucus appears green, an enzyme called myeloperoxidase (which helps reduce acids) and immune cells called neutrophils may be present. Green snot means that your immune system is likely working at full force to battle a viral infection.

If your snot is yellow, white, or green, take it as a sign to get some extra rest and take care of yourself. While you're bearing the brunt of a cold or sinus infection, the ACS recommends seeking relief by taking a medicine specifically designed to relieve symptoms (such as runniness and congestion). However, they also warn that if you use antihistamines and decongestants too often, their effectiveness can gradually decrease. Keep in mind, too, that scientific literature reviews have found little solid evidence that cold medicine actually works—meaning you may be sniffling up a storm until your immune system conquers your infection once and for all.

[h/t Reactions]