Not even the most hardened food lovers can avoid shedding a tear when they chop onions. But why does this happen? In this post, we explain why onions make you cry, along with other interesting facts about onions.
Why Do Onions Make You Cry?
In a way, onions make us cry to discourage us from eating them — but with very little success, obviously!
Jokes aside, the tearing effect of onions is a defense mechanism designed to fend off predators, including us, humans. Here’s how it works, step by step:
- Onion cells contain enzymes known as allinases.
- When you slice an onion, allinases are released and set off a chemical chain reaction.
- Allinases convert the amino acid sulfoxides present in onions to sulfenic acids.
- Sulfenic acids, in turn, are transformed by other enzymes into syn-propanethial-S-oxide, the substance that stimulates our eyes’ lachrymal glands.
So, to sum it up, onions irritate our eyes thanks to a defense mechanism where a chain of chemical reactions produce syn-propanethial-S-oxide, a compound that causes our eyes to water.
How To Prevent Onions From Irritating Your Eyes?
Now that you know why onions make you cry, the natural question is “How do we prevent this from happening?”
The answer is to follow the science. The onion compounds that make you cry are gasses, so the best way to protect your eyes is by staying away from those gasses.
While using onion goggles (yes, they’re a thing!) is an effective, common-sense solution, chilling your onions before chopping them is also effective.
Some suspect that chilling the onions works because the low temperature prevents the eye-irritating gasses from rising and reaching your eyes.
Alternatively, you can also have a fan blowing across the cutting board while you chop onions. After all, the compounds that irritate your eyes are gasses, so the air blown by the fan helps disperse them.
If you are interested in learning more about other interesting food facts explained by science, check out our previous post, “Why Are Carrots Orange?”
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