Why Do Onions Make You Cry?

Don’t you just hate it when you’re chopping onions for dinner and then out of nowhere, your eyes are stinging and you can’t see. They’re burning so bad, you actually have to step away for a second to gather yourself! And as soon as you come too close, the burning and stinging and teary eyes are back with a vengeance. What’s a home-chef to do in this conundrum?

Onion Chemistry 101

It’s hard to cook without onions, but at times it can be hard to cook with them as well! Onions are delicious and add an undeniably savory flavor to many dishes. Another thing onions are good at is absorbing sulfur for amino acids. When onions are cut, the cells are broken which causes certain enzymes to react with the sulfur-rich amino acids.

These compounds create a volatile chemical known as propanethial-S-oxide, which is a lachrymatory agent that creates the dreaded burning sensation when it comes in contact with your eyes. The word lachrymatory derives from the Latin word lacrimāre, which means “to weep” 🤧.

Essentially, this reaction is a defense mechanism against pests that would try to eat the onion in nature. Extremely pungent compounds help repel any animals or insects that might want a bite. This is also what activates their flavor, which is what attracts humans to this extremely fragrant vegetable.

Your brain registers this sensation and triggers a tear response to protect your eyes from being damaged or irritated. It’s possible that some people are more sensitive to onions than others and may experience more severe symptoms such as:

  • Hives
  • Itching
  • Tingling
Chopping red onions on a wooden cutting board with a chef knife

Try these tips when making homemade onion gravy!

How to Cut Onions Without Crying?

Thankfully, humans are not doomed to choose between our sight and delicious onions. Here are some methods to help keep the burning at minimum:

  • Use a sharp knife. It’s always recommended to use a sharp knife over a dull one in the kitchen, especially when cutting onions because it breaks open fewer cells, thus releasing fewer enzymes into the air and into your eyes.
  • Thoroughly rinse prepping surfaces. Rinsing cut surfaces after slicing an onion helps to remove any flavor compounds still lingering around.
  • Chill. You can chill the onion in the fridge or freezer before chopping to slow down the enzymatic reaction.
  • Use different variety. Not all onions are created equal and some varieties are less sulfuric than others. Sweeter onions, like green onions for example, are less likely to burn your eyes than yellow, red, or white onions.
  • Goggles, anyone? Maybe you don’t need actual chemistry googles, but swim or safety goggles are a great tried-and-true alternative! Sure, you may look a little silly but who’s going to care about that when eating a delicious meal?
Sliced red onion on a yellow tabletop

Some other (questionable) suggestions include lighting a match, placing a piece of bread in your mouth, or biting the handle of a wooden spoon. There isn’t much science behind these methods, but definitely share in the comments if any of these worked for you!  

If you’re not looking to update your kitchen wardrobe, you also have the option to create a cross-breeze; either with a range hood, open window or a table fan. This will help keep the irritating enzymes from floating around your immediate airspace. Place the onion in a covered container after chopping to help contain the fumes further.   

While these methods are indeed helpful, there is one caveat – since the lachrymatory agent is an integral part of the flavor creation process, utilizing techniques to reduce it could negatively impact the delicious onion flavor we all know and love. Be sure to keep that in mind if you try any of these methods!

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