Dear William,
There are lots of unpleasant things about being sick. Leaking slimy green snot is near the top of my yuck list.
I talked about it with my friend Linda Eddy. She’s a nurse for kids. She runs the nursing program on the Vancouver campus of Washington State University.
She told me that snot is normally clear. It turns yellow or green when our bodies fight germs that can make us sick.
Snot is also called mucus. It’s a thin, slippery liquid that covers many of the surfaces inside our bodies. You can find mucus in your nose, mouth and eyes. It also lines your stomach, intestines and lungs.
One reason we make mucus is to keep the moist linings of some body organs and openings nice and wet. That keeps them from drying out or sticking together.
The other reason we make mucus is to help keep us healthy. Green mucus is a clue that your body is doing that job.
“Mucus is really sticky,” Eddy said. “That’s good because when irritants like allergens, viruses or bacteria get into our nose, mouth or eyes, the sticky mucus traps them.”
If something that can bug you, like dust or pollen, gets into your body, your mucus traps it. You might even sneeze or cough it out. Sometimes germs—also called viruses or bacteria—get in. Your mucus traps those, too. That keeps germs from getting further into your body.
Some germs get past the sticky mucus. So, your body makes white blood cells to find and destroy those germs.
There are always white blood cells hanging out in your mucus. When your body is fighting germs, extra white blood cells rush to your mucus to help out.
“Sometimes those white blood cells are covered with a green protein,” Eddy said. “The more white blood cells with those green proteins, the more green our snot is.”
The protein looks green because it contains iron—and iron looks green when it’s in a mucus-y environment. That green protein has a big germ-killing job.
When a white blood cell finds a germ, it latches onto it. Then it changes its shape to surround the germ. You can imagine the white blood cell wrapping itself around the germ, so the germ is trapped in a little bubble inside the white blood cell. Then the green protein digests the germ. It breaks it down and destroys it.
Eddy told me the best thing to do when we’re sick is drink lots of water. Mucus is mostly water, so sipping it helps your body make thin, slippery mucus so the white blood cells can do their germ-fighting job.
I guess it s-not so gross after all.
Sincerely,
Dr. Universe