That slimy, gooey substance found up your nose is a mixture of dirt, mucus and other stuff you breathe in. A continuous supply of mucus is produced by the nose and sinuses. This acts as a trap for dirt, pollen and other things. Tiny hairs, called cilia, keep the mucus moving from your nose to your throat, where it's eventually swallowed. It may sound yucky, but without snot your nose would become dry, crusty and stuffed up. The mucus helps humidify the air you breathe and keep your nose and throat moist.