Reading: Scientists finally solve the big mystery — how to cut onions without crying

Scientists finally solve the big mystery — how to cut onions without crying

Last updated: 2025/10/16 at 3:14 PM

News Room Published 16 October 2025

If the thing that’s stopping you from making great curries is the fear crying in the kitchen as you cut up onions then scientists have found a way to save you. New research has revealed that two simple methods to chop the the veg can reduce eye irritation and make the whole experience a lot more painless. So, what’s the secret? (Picture: Getty)

When you cut an onion, it releases syn-Propanethial-S-oxide, a liquid compound found in the vegetable. And this causes a chemical reaction in the eye as it triggers nerve endings in the cornea. This new study, published in the journal PNAS, assessed factors that led to different volumes of liquid being released as aerosols during onion slicing (Picture: Getty)

The researchers cut onions using a special guillotine that could be fitted with different types of blades, and they also painted the onion so they could better observe the cutting process in action. In each trial, the researchers varied the knife size, sharpness and cutting speed, and used a microscope to closely measure the knives before use (Picture: Getty)

They found differences in the amount of onion juice released, and could measure the amount of eye irritation each chop was likely to cause. They said that the sprays were directly linked to the sharpness of the knife and the speed at which each knife stroke cut the onion. So what’s the answer to reducing tears? Using a sharper knife and cutting slower (Picture: Getty)

They wrote: ‘By systematically varying blade sharpness and speed, we find that faster or blunter blades significantly increase both the number and energy of ejected droplets.’ The duller knives seemed to push down on the onion, forcing its layers to bend inward. And as the cut continued, these layers sprang back and forced juice out into the air (Picture: Getty)

Then, as the juice droplets were flung into the air, they turned into smaller drops, which allowed them to hang around for longer. If you cut the onion faster, then that caused more juice, which means more mist to irritate the eyes. They advise: ‘Keep knives sharp and cut gently to spray less.’ The researchers also tested to see if chilling onions before cutting them would reduce eye irritation (Picture: Getty)

So they refrigerated onions at 1°C for 12 hours and compared the results with room-temperature samples, but no differences were found. They suggested that more research needs to be done to look at the effects of temperature on onion cutting and droplet generation. They say their findings could also have important implications for reducing other forms of aerosols and droplets in the kitchen, including splashing that can spread food-borne diseases (Picture: Getty)

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