How the nose slows particles down
Air does not pass through the nose in a straight, unobstructed stream. Its winding passages and ridged surfaces make incoming air change direction. Larger airborne particles, including much dust and pollen, are more likely to strike the moist lining instead of continuing deeper into the lungs. Fine hairs near the nostrils catch some debris too, but they are only the first part of the filter.
That lining produces mucus, a sticky layer that traps particles. Beneath it, microscopic cilia—hairlike structures on the surface of cells—beat in coordinated waves. Their motion carries the mucus toward the back of the nose and throat, clearing the captured material from the breathing passages.
A moving filter, not a disposable one
The mucus conveyor keeps working rather than waiting to be cleared all at once. Most of the material it transports is swallowed without notice; the digestive system then handles it. When the lining is irritated or produces extra mucus, the same cleanup can become more obvious as a runny nose or postnasal drip.
This system reduces the load reaching the lower airways, but it does not catch every particle. Its quiet advantage is continuous maintenance: the nose traps debris and moves it away while fresh air keeps coming in.
