Why do onions make us cry?Cut into an onion, and you'll likely shed a few tears. That's due to a chemical reaction that acts as a sort of defense mechanism for the onion—but with the right method, you can avoid the waterworks.First, a quick look at the aforementioned chemical reaction. Cutting an onion damages its cells, releasing an enzyme known as Lachrymatory-factor synthase. As that enzyme spreads, it converts amino acid sulfoxides into sulfenic acid, which stabilizes as syn-ropanethial-S-oxide. (Don't worry, this isn't going to be on the test.)Syn-ropanethial-S-oxide acts as a lachrymatory agent, and we swear that's the last big word we're going to throw at you. When the agent contacts your eyes, it mixes with your tears to create sulfuric acid, which your eyes interpret as contamination (since, well, it is contamination).To address the problem, your tear ducts go to work, creating enough tears to wash out the chemical. That doesn't immediately make things better, so you may find yourself crying for quite a while.By understanding that chemical reaction, we can prevent it.