Here’s what Professor Hallux has to say:
Noses are pretty grubby places. Almost anything could get sniffed up your nose, and snot – or nasal mucus – is there to help filter the air and trap tiny particles – like a sticky doormat. But that doesn’t explain why it can be green at times. It’s all to do with snot’s germ busting powers!
You wouldn’t know to look at it but snot is a bit of a superhero.
It contains white blood cells, antibodies and enzymes that can kill harmful germs. The green colour comes from an enzyme called myeloperoxidase which is found inside Neutrophils, which are a type of white blood cell. Because there’s lots of Neutrophils in snot, all that myeloperoxidase makes it look green.
And all those trapped germs are a very good reason not to pick your nose – think of all those bacteria on your fingers – yuck! Always use a clean tissue to blow your nose and make sure you throw it away and wash your hands – especially if you have a cold. And an even better reason not to EAT your bogies – no matter how hungry you are!