Why do onions make you cry?

Cut onions make stingy air. You cry because it touches your eyes. Tears wash your eyes clean. Then the sting goes away.

When you cut an onion, it lets out tiny bits that float in the air. Some get in your eyes and sting. Your eyes make tears to wash the sting away, like rinsing soap off your hands. The onion is not trying to be mean; it is just what happens when its pieces are broken.

Onions make you cry because cutting them breaks open their cells, which are like tiny bags. The broken cells mix onion chemicals and make a gas. When that gas reaches your wet eyes, it changes into something that stings a little. Your eyes make tears to rinse it away. Fun fact: chilling an onion first can slow the gas down, so fewer stingy bits reach your eyes.