Your respiratory system is protected by a special type of mucus, known as phlegm. Its job is to protect the lungs from stuff that could get in there, like dust, pollen or smoke. The stuff that makes it to your nose is called nasal mucus, or snot.
Nasal mucus is sticky like fly paper, trapping nasty stuff and flushing it away. How does it work normally, and why does it seem to go into overload when you have a cold? In fact, why is a cold called a cold? James May explains all.
For more videos subscribe to the Head Squeeze channel on YouTube.
If you would like to comment on this video or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.