The Scientific Reason Onions Make You Cry

If you're tired of crying like a baby every time you cut onions, you're definitely not alone. Onions might be delicious in the perfect French onion soup, but cutting them is something most folks would rather avoid. So, what gives? Why do onions seem to have it out for almost everyone? Well, as a matter of fact, the pain we experience is actually the result of the onion's natural defense mechanism! 

When you slice into an onion, you damage its cell walls and open up pockets containing the enzyme alliinase. This enzyme then mixes with chemicals like S-1-propenyl-L-cysteine sulfoxide to create sulfurous compounds. One of these, 1-propenyl sulfenic acid, is then transformed into propanethial S-oxide, a compound similar to tear gas, by the enzyme lachrymatory-factor synthase. Basically, slicing an onion creates a chain reaction that produces an airborne chemical that creates a painful sensation when it comes in contact with your eyes and irritates your tear glands.  

Onions developed this defense mechanism as a way to prevent critters from snacking on them as they grow. Unfortunately for them, humans are persistent, and tears or no tears, we aren't going to stop eating them. Fortunately, there are a few ways to prevent onions from making you cry so you can continue enjoying them without the pain. 

People use many tricks to mitigate the sting while cutting onions, but some can go hand in hand. For instance, refrigerating onions before cutting them can help because the compounds that cause irritation are less volatile when cold. Alongside this, make sure to cut onions in a well-ventilated area or near a fan so that the chemicals can disperse. These two tricks work great together and can make a huge difference. 

Alternatively, you can use Martha Stewart's burner trick. This involves slicing onions as close to an open flame as possible, such as a gas stovetop. While this might sound strange, the idea is that the flame will draw in and remove the irritating compounds before they can reach your eyes. However, because some people have more sensitive tear glands, not every method is one-size-fits-all, and it may take some trial and error to find what works for you. 

That said, if nothing seems to work, not all hope is lost! A "no tears" onion called the Sunion was launched in 2017, following 30 years of hybridization efforts. Unlike other onions, these are said to get sweeter over time, and when dietitian Heather Martin tested them on Today, she reported no burning or stinging, even after putting the sliced onion right under her nose. Sunions are available at select store locations, including Aldi, Kroger, Costco, Publix, Meijer, and Whole Foods.