Why do Onions Make us Cry??

Let's look at it from the point of view of the onion. an onion is perfectly polite to us until we start hacking at it with knife. Alas, the act of cutting enlivens a gas, propanethiol S-oxide, which works in tandem with the enzymes in the onion to unleash a passive Sulphur compound found within the onion. The result : as you cut, the gas moves upwards and, combined with the water in your eyes, creates sulphuric acid.

Your ayes aren’t happy, even if you are, and react in the only way they know how when irritated by foreign substance – they start tearing. Rubbing your eyes with your hands is about the worst way to alleviate the problem, since your hands are likely full of the tear-inducing agent too.