Simply put, snot is mucus that is produced by a special membrane in the nose. The purpose of snot is to trap dust particles, germs and pollen that are inhaled and to prevent them from getting into the lungs. When the inhaled particle and the surrounding mucus that surrounds it dry and solidify, you get what most people call bogeys (or boogers in the USA). Runny noses and copious amounts of snot can be particularly bothersome during the winter. Ailments such as the common cold can lead to increased nasal mucus production but even those in good health can find themselves sniffing and snotting when they walk from the cold outside air into a well heated room. This is because mucus will thicken outside in the cold, but in a heated room the mucus thins and becomes runny. A particularly charming thought to finish on: we actually produce a cupful of nasal mucus every day and much of it ends up getting swallowed!!!!