The sticky stuff that we cough up and call snot is an expert at trapping germs, viruses, dirt and dust from the respiratory tract. And when it turns green, yellow or another color, it may signal that we’re fighting off a viral infection or bacterial disease.
Mucus is constantly on the move, traveling through our sinuses, into our nasal passages, down the back of the throat and into the stomach. This movement prevents bacteria from staying in one place and growing into an infection. Mucus also contains white blood cells, which fight off harmful germs and other debris in the throat and lungs. And if you’re sick with a virus, the white blood cells that float in the phlegm give it its characteristic color.
Most of the time, phlegm is clear and white, but when we’re sick with a cold or other illness that triggers increased production, it can turn yellow or green. The color comes from the inflammatory chemicals that the white blood cells release when they’re fighting off infection.
But a prevailing myth is that we need to take antibiotics if our phlegm is green, and that’s simply not true. Most of the infections that lead to green phlegm are caused by viruses, not bacteria, and will get better without treatment within a few days or weeks. Only if the mucus persists, or it’s accompanied by other symptoms, should you see a doctor and possibly start antibiotics.