Have you ever wondered why chopping an onion makes you cry like a baby? It’s not because you’re emotionally attached to the onion, but because of a chemical reaction that occurs when you cut it open.
Here’s the science behind onion tears.
Onions are bulbs that grow underground, where they have to protect themselves from hungry animals. To do this, they produce amino acid sulfoxides that form sulfenic acids inside their cells.
When you slice an onion, you break its cells and release these sulfenic acids, which mix with enzymes and form a gas called propanethial S-oxide.
This gas is a lachrymatory agent, which means it stimulates the production of tears when it reaches your eyes. The gas reacts with the water in your tear film and forms sulfuric acid, which burns your eyes and makes them water more.
Your brain then signals your lacrimal glands to produce more tears to flush out the irritant.
Now you know why you cry when you peel onions