Why cutting onions makes you cry

You have certainly already found yourself crying when you were just chopping an onion to prepare a delicious meal... But what is the cause of this phenomenon and are there efficient tips to prevent it?

When you cut an onion, the knife blade damages the plant cells, which releases a volatile molecule: propanethial oxide. When it meets the eyes, this gas is transformed into propanesulfonic acid, which is as irritating as sulfuric acid. This compound triggers a defense mechanism to limit the irritation of the eye: the secretion of tears, which cleans the eye to interrupt the irritating effect.

Are there effective ways to stop crying by cutting onions? The answer is yes, here are a few examples: putting the onion in a cool place or in the freezer before cooking reduces the amount of propanethial oxide released because the chemical reaction that causes its transformation is slowed down. Using a sharp knife can also help because it damages fewer plant cells. Of course, wearing goggles is very effective in preventing the irritating compound from coming into contact with your eyes!

Interesting fact: even though they are all salty, the composition of reflex tears, such as when we cut an onion, and those emitted when we are sad, for example, do not have the same chemical composition. Indeed, the latter contain hormones.