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We’ve all been there. You’re about to try the recipe you’ve been craving for ages when you see that one line: “Start by chopping the onions.” Sure, they’re a great flavor enhancer, but onions can also be a pain in the kitchen.
“Onions have a defense mechanism against a lot of different pests and potential herbivores,” explains Brian Quoc Le, a food scientist and food industry consultant. The plant cells, he says, are separated into different compartments. One contains an enzyme, while the other contains a specialized amino acid. When the cells are ruptured by a knife, replicating an insect’s bite, they mix and create a sulfurous compound that reaches your eyes and makes you tear up.
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While the compound isn’t dangerous, the tears can impair your vision at a critical time, while you’re handling knives and other sharp kitchen tools, says Natasha Herz, M.D., spokesperson for the American Academy of Ophthalmology and an ophthalmologist at Family Care and Surgery in Rockville, MD.
This doesn’t mean you should stop chopping onions altogether. We asked experts for their favorite science-backed tips to keep the tears from flowing:
1. Opt for onion goggles
You’ll look goofy, but food scientists and chefs alike say they might be your best option. Onion goggles are designed to fully isolate your eyes from the irritating compounds released by the chopping, therefore preventing the reaction that causes the tears to flow. “Once you get past the part where you look a little funny, they really work,” says Lisa McManus, executive editor at America’s Test Kitchen Reviews. Swim goggles should work as well. Regular glasses and contacts can also help, but they’ll still leave parts of your eyes unshielded. Who cares about what they look like in the kitchen anyway?
2. Create some air movement
Creating some airflow can help, says Abbey Thiel, a food scientist and YouTuber. Opening the window to create a draft can help — even though you can’t predict the direction in which the wind is going to blow. Turning on a fan to try and keep the compounds away from your eyes could keep the tears at bay, although it may not get rid of all the irritating compounds. Having a fan in the kitchen can also be tricky.
3. Cool down your onions
Cold temperatures generally slow down chemical reactions, including the one that happens when you cut onions. Nik Sharma, a molecular biologist turned chef and cookbook author, says he puts his onions in the freezer for 10 to 15 minutes. “I remember hearing stories about how [young chefs in hotels and restaurants] would be kept to sit in cold rooms […] and chop the onions there. It was the same logic,” he says.
4. Use a sharp knife
There’s science behind this idea. “A blunt knife is going to tear away more of the cells of the onion and […] release more of these volatiles,” explains Brian Chau, a food scientist. A sharp knife, conversely, means a cleaner cut and fewer ruptured cells. “I know some people are afraid of sharp knives, but a sharp knife not only doesn’t slide around, when you put it on the food, it cuts through right where you put it and makes chopping things much easier,” McManus says. For more safety, she recommends holding the knife over the spot where the handle meets the blade and holding the blade in a pinch grip between your thumb and forefinger.
5. Dip your knife in lemon juice or vinegar… but be careful
“Some enzymes will denature under acidic conditions. They unravel and lose their function,” Thiel says. (Denature means to change the natural qualities of something.) “This is why you add lemon juice to guacamole to stop the browning, which is an enzymatic reaction.” Since the reaction that causes your eyes to tear up when chopping onions also involves enzymes, dipping your knife into lemon juice, vinegar, or some sort of acid could lessen your chances of crying. However, Chau says, it won’t work all the time, and you’ll have to be extra careful while handling your knife.
Another way to make the conditions acidic enough, Sharma says, is to cut the onion in half and dip it in cold water with lemon juice for two to five minutes. He recommends three to four tablespoons of lemon juice per quart of water.
6. Consider using a food processor
A food processor can make the chopping quick and easy. “One of the factors I really look at when I evaluate food processors is …the pulse button, because it should be brief and violent. It should toss the food and stop when you let go of it,” McManus says. However, some food processors might not chop the onion into uniform pieces, which could lead the onion to cook unevenly, she adds.
7. Don’t cut the root out first
That’s another one of the onion’s defense mechanisms: Cutting the root end of the onion out will signal to the rest of the bulb that it’s under attack, Chau explains. “If you’re trying to dice an onion, what you do is cut it in half where you still maintain [the root at] the bottom. And then you start to slice in different directions without actually cutting off that [root],” he says.
8. Opt for a different kind
Scallions and sweet onions will be easier on your eyes, Chau explains, because they’re typically sweeter and less sulfurous. However, substituting red, white or yellow onions will change the flavor profile of your dish and might prove more expensive, McManus warns. “To get a cup or a half cup of onions, it’s a lot of scallions you’re going through,” she says.
9. Wash your hands
Washing your hands before cooking is good practice, but don’t forget to wash them after cutting onions as well. “It’s easy to forget,” Herz says, “but definitely don’t get the [onion] juice directly in your eyes.” If you do forget, she recommends flushing it out with eye wash, artificial tears or cold tap water.
10. Soothe your eyes if needed
If your eyes still get irritated after trying all these hacks, it’s time to think about ways to find relief. Herz recommends cold, preservative-free artificial tears to help soothe the irritation and calm the bufor a few seconds could backfire by charging up the enzymes inside the onion, Sharma explains. To completely denature them, you’d have to cook the onion for a longer time, which would alter the recipe.
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