Why do we cry when we cut an onion?

There are various home remedies to cut an onion without crying. You can put it in the freezer, put on swimming goggles, use a very sharp knife… But really, why these tears as soon as you cut an onion?

Who is the culprit behind our tears?

The culprit is an acid called syn-Propanethial-S-oxide. When the onion is cut, some of its cells break. Compounds then present in these cells are released. Two of these compounds react to form the acid in question. However, this acid takes the form of a gas and spreads through the air and comes into contact with our eyes. And that’s not all! Once the acid comes into contact with our eyes, another reaction occurs and sulfuric acid is formed. Sulfuric acid is irritating and our body produces a liquid to clean our eyes and get rid of it… That’s when the tears come!

What substances are responsible for our tears?
Credit: Pixnio.

How do you stop crying when cutting an onion?

So do grandma’s remedies have any truth to them? Yes for some that even have a scientific explanation. For example, putting the onion in the refrigerator or in the freezer limits the amount of acid that is released into the air. In fact, the cold slows down the action of the enzyme responsible for the formation of syn-propanethial-S-oxide. By removing the end close to the roots, some of the acid is extracted. By using a sharp knife, you also cut the onion cleanly, and therefore break fewer cells and release fewer compounds. Finally, for the glasses, in a rather obvious way, they prevent the contact of the gas with the eyes.

Read also: Weeping cells have been grown in the laboratory

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