One of the most notorious parts of your upper-respiratory tract is mucus, the thick, slippery coating that lines your breathing passages all the way to your lungs.
Mucus scores high on the list of Topics to Raise If You Never Want to Be Invited Out Again. However, biology nerds know there are many reasons to love your mucus. It plays essential defense and clean-up roles in your respiratory system, trapping nasty substances—from pollen and dust to bacteria and viruses. Without mucus, your nose would be in a perpetual state of dry discomfort, and you’d certainly be at more risk for nose and throat infections.
Many people associate mucus with colds and respiratory problems. While these conditions may cause your body to produce more mucus, they’re more likely to thicken your existing mucus and inflame your airways, disrupting your body’s normal mucus-disposal system and making you increasingly aware of the slimy stuff.
If you’re an average person, your respiratory system produces a healthy four cups of mucus over the course of a day. Ordinarily, the mucus in your nose collects airborne contaminants and flows silently down the back of your throat and into your stomach. Your stomach then digests this mucuscoated garbage. This design highlights the power of your stomach’s digestive juices. It also suggests that, when faced with dirt and disease-causing compounds, it’s often safer to eat them than to inhale them.
Source of Information : Oreilly - Your Body Missing Manual