While what I am about to say is trivial and unproven, it is still worthy of saying it.
I am a great fan of onions, and like to include them in my cooking whenever possible. Ironically, I also have a great problem when it comes to chopping them, because my eyes water and burn like hell. Of course, everyone has trouble when it comes to chopping onions, but for some reason, I seem to suffer from the eyes burning for much longer and harder than others. While the rest seem to get through it in a few minutes, I seem to suffer from the burning in my eye for nearly an hour or more.
So like everyone else, I googled for remedies….and there were a ton of them. Some of the common ones were sticking your tongue out while chopping, chewing gum, freezing the onion, among others. But none of these grandma methods were really a good solution, 'cos none of them had any logic or theory behind them. So I went about trying to figure out why eyes burn in the first place when you chop onions. And I am going to answer this question below.
Simply put, eyes burn when chopping onions because, there is some substance that comes out of the onion, travels through the medium (air) and comes in contact with the eyes. This substance causes a reaction from our eye, that causes the burning. First, lets eliminate the obvious possibilities.
It cannot be some liquid squirting out of the onion, because, if so, my eyes shouldn’t burn at all since I wear glasses all the time.
It cannot be fumes that come in contact with your eye when you chop. I have tried squinting my eyes, keeping my eyes open at a minimum while chopping. If it was due to surface contact, that must have atleast reduced the burning. It dint.
Its not by contact. Its not by spraying liquid. So what else could it be? How else could these fumes be transmitted? The only that means that sounds logical is by means of inhalation. The air contains the fumes. We breathe in that air. These fumes get into our eye through the nostrils. That is the only remaining way in which the fumes can come in contact with our eye.
To test this, I tried to chop onions by avoiding inhalation at the time I chop. I took a deep breath, and started chopping half an onion while breathing out. Then, I moved away, took a deep breath, and returned to the chopping. I could certainly feel the difference. My eyes hardly burnt when compared to the times before.
So, if you want to chop onions without your eyes watering, practice yoga. Develop control over your breathing. If you can hold your breath for long periods of time, you can chop these bastards with this simple technique.