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Dec.—It may seem like a minor domestic drama, but science has finally explained why an onion can turn anyone into a sea of tears. Researchers at Cornell University (USA) demonstrated that when cutting an onion, microdroplets are released at extremely high speeds that carry the irritating compound responsible for eye stinging, revealed the magazine Earth.com.
That compound is propanethiol S-oxide (also called thio-propanal sulfoxide (C3H6OS)), the so-called "tear-inducing substance" of the onion. What is novel about the study, published in the Proceedings of the National Academies of Sciences (PNAS), is not only identifying it but showing how it reaches the eyes so quickly: when the knife presses the inner layers, pressure builds up until the outer skin breaks and the onion literally 'explodes' in an invisible cloud of irritating particles. According to scientists, these droplets can be ejected at speeds that far exceed the movement of the knife itself.
"We discovered that the speed of the mist coming out is much greater than the speed of the blade when cutting," said Sunghwan Jung, lead author of the study and professor of biological and environmental engineering at Cornell University.
Why Do Onions Make Us Cry?
High-speed cameras used by the research team allowed them to see what is normally impossible to observe with the naked eye: a microscopic burst that travels through the air with enough force to reach the eyes within seconds. And this not only explains the tears; experts also warn that this mechanism can help disperse bacteria present on the surface of the food, adding a food safety component to the issue.
When an onion makes us cry, it is actually its way of 'telling us' that it does not want to be eaten. It is a biochemical defense mechanism that begins when the plant absorbs sulfur from the soil and stores it as a compound called 1-propenyl-L-cysteine sulfoxide. When the onion is cut, this compound reacts with enzymes and forms syn-propanethial-S-oxide, the well-known 'tear factor,' which is released in an aerosol of tiny droplets at high speed. Upon contact with the moisture in the eyes, this chemical causes a mild formation of sulfuric acid that irritates the tear glands, causing tears.
How to Avoid It
But the good news is that science has also found the remedy. The study points out that cutting onions more slowly and with sharp knives reduces internal pressure and therefore decreases both the amount and speed of the irritating droplets. They even suggest that applying a thin layer of oil before cutting could help block some of the dripping.
In summary: there is no need for extravagant tricks or home theories. The scientific answer is already on the table: less force, more precision, and patience.
(Taken from RT in Spanish)
