When you cut an onion, a very small amount of sulfric acid in onion juice burns our eyes and secretes tears by running the defense system.
Some cooks recommend that wet before cutting the onion, keeping wet while cutting or cutting the onion under the water flowing from the tap.
Another opinion recommends to breathe orally when chopping the onion. According to this view, instead of entering our nose with our gas breath and approaching our eyes, it enters our lungs directly. Meanwhile, the smell of onions entering your lungs is not harmful.