Tearing up while chopping onions is a familiar kitchen struggle—but now, thanks to a team of scientists at Cornell University, we know how to make the process a little less painful.
In a recent study, a group of physicists, biologists, and engineers investigated what causes onions to release the eye-irritating spray that brings on the tears—and how to reduce it.
We already know that the culprit behind onion-induced crying is a compound called syn-propanethial-S-oxide.
This chemical is released into the air when onion cells are damaged, and it irritates the eyes, causing them to water.
But until now, no one had looked closely at the physical mechanics of onion cutting to see what makes this effect worse—or better.
To get to the bottom of it, the research team designed a clever experiment. They created a special onion-cutting machine—essentially a guillotine that could be fitted with different types of blades.
They coated pieces of onion with paint so they could closely watch how the layers responded to slicing.
Then, using high-speed cameras and even an electron microscope, they examined how different blade sizes, sharpness levels, and cutting speeds affected how much onion juice was sprayed into the air.
Their findings were surprisingly clear: using a sharp knife and cutting slowly significantly reduces the amount of irritating spray. A dull knife tends to crush the onion more than slice it, pushing its layers inward.
When the blade finally breaks through, the compressed layers spring back and fling onion juice into the air—right toward your eyes. This juice often breaks into tiny droplets that can stay suspended in the air longer, increasing the chance of irritation.
On the other hand, a sharp knife makes cleaner cuts that disturb the onion less, releasing fewer droplets. Slower cuts also create less turbulence and less juice overall, helping to keep your eyes dry.
So, if you want to cut onions with fewer tears, science now has a simple answer: keep your knives sharp and take your time. It might not make the onion smell any sweeter, but it will definitely make the process a little more comfortable.
The team’s findings are available in full on the arXiv preprint server, adding a bit of scientific insight to one of life’s everyday annoyances.
If you care about nutrition, please read studies about the harm of vitamin D deficiency, and Mediterranean diet may preserve brain volume in older adults.
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