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- When you cut into an onion, it releases irritating chemicals into the air that make your eyes water.
- There are tons of theories about preventing onion tears, but only a few are effective.
- Experts recommend using a sharp knife when cutting, refrigerating your onions, or investing in special gadgets.
It's happened to the best of us: you're in the kitchen, chopping up onions for your dinner, when suddenly, tears are flowing and your eyes are burning.
"All foods have some defense mechanism," says Brian Chau, a self-employed food scientist and food systems analyst who holds a Master's degree in food systems and society from Oregon Health & Science University.
Onions have evolved over time to become tearjerkers, but preparing such a delicious — not to mention common — ingredient doesn't have to be a sob story. Once you understand why onions make you cry, prevention is relatively simple.
"Some people are more sensitive to [onions] than others, which may make them produce more tears," says Chef Julie Andrews, MS, RDN, CD, FAND, and creator of The Healthy Epicurean.
Why do onions make you cry?
Onions' tear-causing properties are more than an annoyance. "Onions have developed a biochemical pathway to protect themselves from predators," Chau says. When you cut into the cells of an onion, they release the enzyme alliinase along with a family of compounds known as cysteine sulfoxides, Chau says.
Through a series of subsequent chemical reactions, a volatile gas called propanethial S-oxide is created and spreads through the air.
"The body's reaction to the gas touching the surface of the eye is to create tears to flush the gas out of the eye," says Andrews. Not all onions are equally irritating though: sweet onions and scallions contain less sulfur than red, white, and yellow onions, so they tend to result in a smaller reaction.
4 tried and true tips to prevent you from crying
Scientific solutions are out there, but a quick online search for onion remedies may lead you to "hacks" that are more grounded in optimism than in biology. In order to ward off or reduce tears, you'll need to prevent the irritating gas from being released in the first place, or prevent it from reaching your eyes.
These expert-approved tips are ranked from easiest to hardest, but note that because everyone has a slightly different reaction to onions, some techniques may be more effective than others.
1. Use a sharp knife
Keeping your knives sharp is generally good practice, but particularly important when working with onions. "A sharp knife causes less damage to the onion flesh, reducing the amount of gas that is released," Andrews says.
A dull knife will only make slicing and dicing more difficult, and will increase the amount of time you spend around volatile gas, Chau says. Investing in a knife sharpener or picking up a new set of blades may not completely prevent crying, but it could keep it from becoming a total sob fest.
2. Refrigerate your onions in advance
The only thing that this tip requires is enough foresight to stick your onions in the fridge before you start cooking. "This is perhaps the best method to try," Andrews says, and Chau agrees: "Chemical reactions slow down under colder temperatures."
Place your onion in the refrigerator for 30 to 45 minutes, and remove when you're ready to start slicing. Try to work quickly — as your onions warm up, you may feel your eyes start to sting. Note that keeping onions in the fridge long term can cause them to spoil more quickly, so you should only use this method when you plan to use your onions right away.
3. Use eye protection
If you're still struggling to get through meal prep, try creating a barrier between the gas and your eyes. Standard eyeglasses or sunglasses can help, but Chau says that eye protection with a seal will be most effective for keeping gas out. Specialized onion goggles are available and may be worth it just for the laughs, but swimming or safety goggles can also work well.
4. Use alternative kitchen tools
If you have the means, Chau recommends investing in specialty gadgets. "Buy a good food processor that has an attachment to dice or slice," he says. "You reduce the chances of crying because your exposure time is lower and sometimes, the onions are in a closed environment." A lower-cost alternative is a vegetable chopper, which you can use with almost any type of produce and will save you a ton of time on prep.
Debunking common hacks that don't actually work
- Chewing gum. Some people swear by this, but Chau says there's no scientific reasoning to support this hack because it doesn't protect your eyes or prevent the onion from releasing gas.
- Soaking your onions in water. According to Chau, water will only accelerate a tearful reaction, and Andrews notes that tossing soaking wet onions into a pan could cause hot oil to splatter and burn you.
- Holding your breath. Breathing in the irritating gas released from your onions doesn't cause tears, Chau says — it's the reaction the gas causes when it hits your eyes. Not to mention the dangers of holding your breath while handling a sharp knife.
- Microwaving your onions before cutting. Using heat actually worsens the gaseous reaction, according to Chau, and could change the taste of your onions.
When you cut into an onion, it releases chemicals that irritate the eyes and cause you to cry. There are lots of phony hacks out there, but to reduce your chances of tears, use the sharpest knife possible and chill your onion in the fridge in advance. If all else fails, using eye protection or investing in specialty kitchen gadgets will keep you from becoming a weepy mess.