You blow your nose, out comes snot. Five seconds later, you're stuffed-up again. Where is all this mucus coming from?
When it comes to science questions, we like to consult kid-friendly sites. (As English majors, we need simple answers.) Fortunately, Kidzworld fits the bill. The site explains that snot comes from mucus membranes that line the inside of your nose. The membranes secrete mucus in order to protect you from dust, germs, and pollen. The snot traps all this nasty stuff so it doesn't get into your lungs.
As Ask Dr. Universe informed us, the mucus acts like a shower inside your nose, washing away dead cells and germs. When you have a cold, even more mucus forms to get rid of the germs as quickly as possible. Unfortunately, this can result in too much mucus, blocking the air passages and leading to a stuffed-up nose.
Still, the occasional clogged schnoz is a small price to pay for ridding your body of germs. Three cheers for snot! Drip, drip, hooray! Drip, drip, hooray! Drip, drip, hooray!