Tears keep the eye surface clean and wash away small irritants throughout the day.

The longer version

Tears bathe the surface of the eye with a thin, continuously renewed film. Glands above the eye produce a watery layer that carries oxygen to the clear front surface and flushes away dust, pollen and shed cells. A layer of mucus underneath helps the film cling to the eye, while a thin oily layer on top slows evaporation.

Each blink spreads the mixture evenly and pumps the surplus toward tiny openings at the inner corner, which drain into the nose. The film also smooths tiny irregularities in the surface, which improves optical clarity. Irritants trigger a much larger flow, which is why an eyelash or a speck of grit produces sudden watering.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.