Answer:
It is how our body usually reacts to code or allergies. Mucus, or snot, acts like a defense against infection because when you have stuff like a cold your nose and sinuses are more vulnerable to a bacterial infection. So it is like our bodies getting rid of what is causing your cold or allergies in the first place.
Step-by-step explanation:
I read a book on this. I might not be right, but hope this helps!!! :D