Mucus

Nose hairs trap particles, while sticky mucus traps pathogens, helping prevent them from reaching the lungs.

The airways must let air enter, so they cannot be sealed like the skin. Instead, sticky mucus in the nose, trachea and bronchi traps pathogens carried in inhaled air. Cells lining the trachea and bronchi have cilia, microscopic hair-like structures that beat to move this mucus towards the back of the throat.