Why onions make you cry and what you can do to stop it

If you’re a seasoned home cook, chances are you probably cry a lot. Not because of the failed recipes or ruined cookware, but because of onions. Chopping onions is one of the first steps in a lot of recipes. But slicing and dicing the root vegetable can cause stinging eyes, tears, and a runny nose. But why do onions make you cry, and what can you do about it?

It all boils down to science.

When onions are growing underground, they absorb lots of sulfur from the dirt. You may know sulfur as the chemical behind unpleasant smells like rotten eggs. The onion turns the sulfur into amino acids called sulfoxides, which it uses as a defense mechanism to protect it from being eaten by animals. 

This works as a defense mechanism because when an onion breaks apart—from being chopped or being bitten into—the sulfoxides react with the onion’s enzymes to make sulfenic acid, which gets rearranged into a chemical compound called syn-propanethial-S-oxide. Now that’s a mouthful!

The syn-propanethial-S-oxide creates an irritating gas that floats up to your eyes, who then use their own defense mechanism of tears to flush out the foreign gas. 

While onions aren’t dangerous to your eyes, tears in the kitchen can be an inconvenient part of the cooking process. So what can you do to reduce crying from onion irritation?

Try chilling your onion in the fridge beforehand. A colder temperature slows down the chemical reaction that releases the gas and causes crying. You could also chop your onion while it’s submerged in water. This will dilute the gases and reduce their strength. 

Similarly, this TikTok hack uses a wet paper towel for tear-free onion-cutting. 

Alternatively, Healthline recommends putting some distance between you and the onion, or some kind of barrier—like goggles—to block the traveling gas from your eyes. 

If all else fails, you’ll just have to grin and bear it. There’s no use crying over chopped onions. 

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