Why do onions make us cry?
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Transcript
Have you ever seen tears pop out when someone cuts an onion? Why do onions make us cry?
When an onion is cut, its tiny cells break open. They let out an invisible gas that floats up.
The gas reaches your eyes and makes them sting a little. Your eyes notice and start making tears.
Tears wash the sting away and keep your eyes comfy. That is why onion-cutting can make you cry.
So that's why onions can make us cry. Their invisible gas tells our eyes to make washing tears!
For grown-ups: the science
Cut onions send an invisible gas to your eyes, and your eyes make tears to wash it away.
Cutting an onion ruptures its cells, allowing enzymes and sulfur-containing compounds to react and form syn-propanethial-S-oxide, a volatile eye irritant. Tears are produced as a protective reflex that helps dilute and wash away the irritant.