Here's a bit more about it:

* Formation: When you cut or crush an onion, cells are broken, releasing enzymes that convert a precursor compound called alliin into propanethial S-oxide.

* Irritant: This compound is a volatile sulfur compound that irritates the eyes, causing them to water.

* Flavor and Aroma: Propanethial S-oxide is also responsible for the strong, pungent flavor and aroma of onions.

Let me know if you have any other questions!