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Cut an Onion Without Crying With This Trick

Save the safety goggles for science experiments and learn this easy way to chop onions without the tears.

Cross section of an onion
Avoid tears when cutting onions.
James Martin/CNET

This story is part of Try This, CNET's collection of simple tips to improve your life, fast.

Several years back, I was at my brother's birthday party when a fellow guest -- and chef -- gave me one of the best food preparation tips that I'll never forget: the proper way to dice an onion.

I've been using his technique for years now and it definitely makes dicing onions easy and neat. However, just recently I learned there's a big bonus -- fewer tears while cutting the onion. I almost never cry when cutting an onion with this method, and if I do, it's usually because I goofed up.

See my trick below for quickly dicing an onion and learn why it prevents tears, along with some other ways to avoid crying while cutting onions if you are particularly sensitive. For more tips around the kitchen, here's how to avoid jabbing yourself while pitting an avocadomake a cake without a pan and cut a cake without a knife. Also, for safe slicing and dicing be sure to check out our picks of the best chef's knives and best direct-to-consumer knives.

Why do onions make us cry?

Onions are in the allium genus of flowering plants that includes garlic, leeks, shallots and chives. They grow as bulbs under the ground and include toxic substances in their roots to protect themselves from moles and other underground pests. Those toxins are strong enough to poison cats and dogs.

Not to get too technical, but onions take sulfur from soil to create amino acid sulfoxides. When an onion is cut, those sulfoxides combine with other enzymes in the onion to create sulfur gas. When that gas interacts with the moisture around your eyes, it creates sulfur dioxide, which burns and causes your eyes to water.

How do I dice an onion without crying?

Most of the onion's sulfoxides reside in its root -- the round part with hairs at the bottom of the onion. If you can leave the root untouched, you'll significantly reduce the amount of chemicals that make you cry when cutting.

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One simple method is to chop off the root end and then discard it when you start. You can then dice the rest of the onion however you like. 

This way works fine, and if you want to stop there, great. But I think my method is even better because it avoids dicing the root while letting you easily work with the rest of the onion.

First, cut the onion lengthwise, from tip to root. (Yes, this will cut the root in half, but it's the only time you will cut it.) Then remove the inedible outer layers, and slice off the tip of one half.

Now you're ready to dice. Make a series of slices across one of the halves horizontally, starting half an inch from the top. Most importantly, stop slicing before you reach the root, so you leave the onion connected at the root end.

Next, make a series of vertical cuts with the tip of your knife pointing toward the root, starting at one side and moving to the other. Again, don't cut into the root end -- slice down the onion with the tip of your knife stopping short of the root. Careful: These cuts provide the biggest chance for making a mistake and accidentally slicing the root.

To finish dicing the onion, make a third series of slices starting at the end farthest from the root and moving your knife gradually closer with each cut. These slices will separate your diced pieces from the rest of the onion.

Finish your final vertical slice right before you reach the root, which can be tossed, leaving you with a nice, neat pile of diced onion. Repeat this process with the other half of the onion to finish your preparation.

What are some other ways to avoid tears from onions?

I wear contact lenses, which offer protection against onions' sulfur output, so I am less susceptible to crying when cutting. If you try my dicing method and still find yourself in tears, there are a few other tricks you can use to reduce the effect.

First, try refrigerating your onions briefly before cutting them. The National Onion Association recommends chilling onions for 30 minutes before preparation. The colder temperature will slow down the sulfur gas, it says, causing less reaction with your eyes. (The organization also recommends keeping the root intact.)

Next, try sharpening your knife. A dull knife will smash the onion more than a sharp one and may release more of the offending sulfoxides.

Lastly, if you're still crying, try cutting your onions under a ceiling fan or kitchen vent. Both may help dissipate the sulfur gas before it attacks your eyes.

If you're looking for more tips, here's how to get rid of junk mail, see what's coming in the mail and start a fire with Doritos.