Onions: the tear-asking veggie

I am on a roll here, just wanting to explain everyday experience. I am researching for a series. Coming soon. Anyway, here’s the post.

Chopping onions feels like a battle—your eyes water, your nose stings, and you wonder why cooking dinner suddenly turned emotional. But there’s a neat bit of chemistry behind those tears.

Inside an onion’s cells are compounds that stay harmless until you start cutting. When you slice through, you break the cells open, and enzymes mix with sulfur-containing molecules. This reaction produces a volatile gas called syn-Propanethial-S-oxide (quite a mouthful). When this gas reaches your eyes, it reacts with the water in your tears to form a mild sulfuric acid. Your eyes don’t like acid, so they send out more tears to wash it away—hence, the crying.

Luckily, there are tricks to fight back. Chilling the onion before cutting slows down the enzymes, so less tear-inducing gas forms. Cutting under running water helps wash away the compounds before they hit your eyes. And a sharp knife does less cell damage than a dull one, meaning fewer chemicals are released.

So the next time your eyes water in the kitchen, you can thank chemistry. The onion isn’t making you emotional—it’s just running a tiny lab experiment on your face.