Why Cutting Onions Makes Us Cry and Tear-Free Tips for Cutting Onions

By Erin Marissa Russell

Everyone knows that slicing onions comes along with the side effect of bringing tears to the eyes of the chef. But have you ever wondered what it is that makes onions such a tearjerker? And since people are so prone to tears when cutting this vegetable, what can you do to make the process easier and cut your homegrown onions without triggering tears?

Why Cutting Onions Makes Us Cry

Every onion contains sulfeoides, which are amino acids that, within the cells of the onion, manufacture sulfexides. As your knife passes through the layers of an onion, the tiny cells that make up the plant are broken open, freeing the standard cell enzymes that were inside. Once they’re airborne, those enzymes combine with the sulfenic acids to transform into the volatile gas propanethial S-oxide, a sulfur chemical.

As you’ve probably experienced for yourself, propanethial S-oxide affects us in much the same way as tear gas. Cutting onions can be so excruciating because when the propanethial S-oxide mixes with the naturally occurring water in your eyes, it generates sulfuric acid.

Once your cornea detects the burning presence of that acid, it sends a signal to your brain to open the floodgates in the lacrimal gland, which is responsible for creating reflex tears. (As their name suggests, unlike the basal tears that keep your eyes hydrated, reflex tears occur in response to eye irritation.) The tears that fall when you’re slicing an onion are actually your eyes’ attempt to clear away this tear jerking chemical by diluting it, then rinsing it off their surface.

You may not have noticed that your crying doesn’t last the entire time you’re working with onions. The first teardrops will usually fall within about 30 seconds from the time you start to chop your onion. And although those tears may come hard and fast, they’ll begin to abate after just five minutes. However, those five minutes can be quite uncomfortable, not to mention an impediment to your vision—not the best situation when you’re working with blazing hot pans and razor sharp cutting tools,

Tear-Free Tips for Cutting Onions

Even though onions have evolved to bring us to tears, there’s no reason for every recipe you make that includes onions as an ingredient to kick off a crying session. Lots of chopping methods to avoid the tendency of onions to make our eyes water exist, although some are much more successful than others (and a few are simply old wives’ tales with no basis in fact). Read on to find out the ways people have come up with to let them slice onions tear-free. You’re sure to find a method that suits you.

Save cutting the onion’s root end until last.

The root end of the onion contains the highest concentration of those troublesome enzymes that cause tears, so the longer you wait to break the layers near the root, the longer you can chop tear-free. Some people simply wait until the very end of the process to tackle the root end, while others take a slightly different approach, slicing off the root end first and running it under cool water to rinse away the milky white juice that seeps from its layers.

Make sure your knife is sharp when you set out to chop onions.

The sharper the knife you use to slice an onion, the fewer of the tear-jerking enzymes you’ll set free to become the volatile gases that often irritate our eyes when the onion is sliced and those enzymes reach the open air. Be sure to select a knife for chopping onions that features a flat blade, not a serrated edge, as a serrated knife will have the opposite of the desired effect. Not only is a dull knife more dangerous in the kitchen because its more prone to cause you to cut yourself, a blade that’s less than sharp will also crush more of the onion’s cells as you chop.

That’s why using a dull knife to chop onions is bound to end with a kitchen sob session. Working with a dull knife results in the onion’s cells emitting more of the enzymes that cause tears than they will when broken with the quick, gliding slice of a sharpened knife.

For tasks like chopping onions when a sharp knife is a requirement, consider honing your blade on a sharpening steel before each use. This guide from Cook’s Illustrated will show you how to sharpen and hone your knife like a pro before you start slicing and dicing.

This next bit may be common sense, but the quicker you chop the onion, the less time you’ll be exposed to the chemicals that cause tears. However, it’s imperative that you use proper knife technique to keep yourself safe while you’re working quickly with a sharp blade. In this video, Gordon Ramsay shares a technique to efficiently and safely chop an onion finely into small cubes.

Limit your exposure to chopped onions.

This one’s practically a no-brainer once you’ve heard the idea. As soon as a section of onion is chopped, pop it into a covered container or slide it into your preheated cooking pan. The less time chopped onions are sitting around with their cut surfaces exposed to the air, the less of the propanethial S-oxide is likely to make it to your eyes to trigger a reaction.

Chill onions in the freezer 15 mins before starting your recipe.

When you lower the temperature of an onion you’re working with, you’re actually freezing the enzymes inside the onion’s cells. As a result, the frozen enzymes can’t combine with the sulfenic acids as they usually would, so the chopped onion never produces any propanethial S-oxide. No propanethial S-oxide, no tears.

Use kitchen ventilation.

Don’t underestimate the power of air to move those propanethial S-oxide fumes out of your vicinity where they can’t cause you any trouble. Some home chefs say that switching on their ventilator hood and working underneath it resolves their onion-slicing woes. Other people have found that plugging in a fan and pointing it toward where you’ll be working is enough to keep the propanethial S-oxide moving so there are no more tears.

Delegate the task to an unfeeling machine.

If you have a food processor or a manual or electric food chopper, there’s no reason to subject yourself to the tears that go along with chopping onions. Simply use the chopper or the appropriate setting on your food processor to cut your onion into pieces of the desired size. If you’re dicing onion in a food processor, be sure to use the appropriate setting so that your chunks are uniformly chopped but not pulverized. By keeping the onion bits under wraps in the bowl of the processor or chopper until they’re ready to use, you’re trapping those pesky compounds that bring tears to your eyes inside along with the onion.

Use water to mask or rinse away the troublesome onion chemicals responsible for tears.

There are a few different approaches that rely on water to keep tears at bay when you’re chopping onions. One method requires a bit of forethought: soaking the onions in water for at least 30 minutes prior to chopping them. Proponents of this method say that soaking the onions causes the propanethial S-oxide to be captured by the water, so it never reaches the air or your eyes in the first place.

There are lots of other tips for reducing tears when you chop onions that use water. Some chefs do their chopping completely underwater. Others apply the water to themselves instead of the onion—though reports of these approaches are anecdotal and we couldn’t confirm their success. You might try holding water in your mouth while you chop, wetting down your forearms, washing both the knife and your onion with soap and water before you begin slicing, draping a wet towel over your neck or under the cutting board, and putting an ice cube in your mouth. (If you try one of these methods, leave us a note in the comments to let us know how it worked for you.)

The simplest solution: Strap on some goggles.

You may look a little silly donning sports or old-school swimming goggles (or even specialized onion goggles like these) before going to work to dice an onion, but it’s not silly if it works—and home chefs and experts alike confirm that this trick works.

To be absolutely clear, chopping onions only results in tears when the onions are raw. Once the onions have been cooked, the enzymes required to create the propanethial S-oxide responsible for your tears will be inactive, so your eye-watering response won’t be triggered.

Dr. Michelle Carter-Caldwell for Vision Service Plan reminds readers to keep safety in mind even with a task as seemingly innocuous as chopping produce. Be careful not to wipe your eyes with your fingers once they’ve been contaminated with onion juice.

When your chopping job is done, wash your hands well to remove any residue the onion may have left behind. And if a drop or two of onion juice actually lands in your eye (causing tears more substantial than mere chopping), you can either use an eye rinse designed for washing out irritants or simply flush your eyes with cool water. If these measures don’t do the trick and you’re still suffering after a few hours have passed, make an appointment to see your eye doctor as soon as you can.

What is your go-to remedy for tear-free chopping when you’re cooking with onions? Do you light a match, turn on a gas burner and cut next to it, rub your cutting board with cut lemon, or adjust your breathing? Have you tried to stack several methods and found a favorite combination that works for you to prevent crying into your onions? We’d love to hear how you’ve been keeping the tears at bay when you chop onions—and how well your technique works compared to the ones we’ve discussed above. Join the conversation in the comments!