Why Do Onions Make Us Cry?

Sometimes a strange but simple fact—that onions make you cry, for example—is so accepted that you forget to ever stop and wonder...why? That is, until you're chopping with a 3-year-old who gets mad at you because you made her weep for no reason. For example.

How Does It Work?

So what's going on with onions that make you cry, or make you shell out $20 for a pair of onion goggles? As Eric Block, author of the book Garlic and Other Alliums (onions are part of the plant genus allium) explained to NPR, "the onion is a perennial bulb that lives in the ground with lots of critters who are looking for a snack." And so they have a chemical defense system, which, like a skunk fending off predators with a stench, releases the tear-jerker chemical to protect itself from being eaten. Within each cell of an onion is a sealed vacuole filled with enzymes that rupture when cut into. The enzymes then mix with other chemicals in the onion cell and, in Blocks words, "a whole cascade of chemical processes happen within an instant."

The result of all those chemical processes are syn-propanethial-S-oxide molecules, the irritating culprit making you (or your 3-year-old) cry. "[It] really is quite beautiful from a scientific viewpoint," Block said.

Smart Graphic

So, What Can I Do?

You've probably heard plenty of tips: Hold a silver spoon in your mouth, hold a piece of bread in your mouth, cut the onion underwater, use a super sharp knife... But Block's tip is simple, and makes plenty of sense once you understand the onion science. "If you just cut the onion in a stream of air blowing away from your face," he says, "then you'll pull the molecules away and they won't get to your eyes."

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Watch 'Em And Weep: Videos About Onions and Tears

Why Do Onions Make Us Cry?

Scientific American breaks it down even more.

Key Facts In This Video

  1. Cutting an onion ruptures its cell walls, releasing enzymes that bind to other compounds to create the lachrymatory factor. 00:21

  2. When the lachrymatory factor gasses waft into the eyes, neurons signal tear production to wash out the potentially harmful chemical. 00:51

  3. Researchers in Japan and New Zealand have collaborated to create a tear-free onion. 01:39

Onions, Emotions, And Why We Cry

Not all tears are the same.

How To Chop Onions Without Crying

Tip 1: Use a sharp knife.

Written by Curiosity Staff December 22, 2016

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