ELI5: Why do onions make us cry?

41 views Feb 23, 2026 2 min read

Imagine you're playing with your toys, and someone accidentally breaks one! That's kind of what happens when you cut an onion.

The onion has tiny, tiny little bags inside, like water balloons. When you chop the onion, you pop those bags open. Inside these bags are special helpers. When the bags break, these helpers mix together and make a special gas called a lachrymator. Lachrymator means "tear-maker."

Here's what happens step-by-step:

  • You cut the onion: Tiny bags break open.
  • Helpers mix: These helpers create a special gas.
  • Gas floats up: The gas floats up into the air, and towards your eyes.
  • Gas meets your eyes: This gas reacts with the water in your eyes.
  • Ouch! A tiny sting: This makes a very, very small amount of acid. It's not dangerous, but it stings a little.
  • Your eyes make tears: Your eyes try to wash away the sting, so they make tears! That's why you cry!
Think of it like this: the onion is trying to protect itself, and the gas is its secret weapon. But don't worry, the tears are just your eyes being helpful and washing away the tiny sting! There are tricks to help prevent the gas from getting to your eyes, like cutting the onion under running water or wearing goggles, but the onion will always have its secret weapon ready!

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