system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you have a runny nose/cold, where does all that never-ending snot come from?
gpt
Snot or more generally "mucus" is formed from relatively small amounts of proteins along with a bunch of water. If you let mucus dry out you can see that it is about 95% water.

Special glands produce mucus from proteins and water pulled from the blood. You need to drink more water when sick because you are losing more than usual through such excretions.