There exists a strange but true fact of life that it’s hard to hold back tears while slicing onions. But the reason why onions make your eyes water is not easy to explain. Check out to find the answer below:
Lindsey du Toit, a scientist at Washington State University said about this fact: “It’s not the onion itself that makes us cry,” she explained, “but a chemical reaction that starts when you cut into it.”
When onions are chopped, it ends up breaking cells within the onion, which release certain enzymes. These enzymes then react with the sulfur, creating amino acid sulfoxides. These, in turn, create the highly unstable syn-propanethial-S-oxide, which is a combination of sulfuric acid, sulfur dioxide and hydrogen sulfide.
When this substance, in a gaseous state, comes in contact with the moisture in your eye, it triggers a burning sensation via the ciliary nerve. When the brain gets a message that there is an irritant in the eye, such as the above, it then kicks the lachrymal glands into overdrive, trying to flush the irritant out of your eyes with tears.