Cutting an onion under water will prevent the sulfuric compounds from reaching your eyes and causing you to tear. If you want to try this method, take safety precautions — use a wide, flat dish to provide maximum workspace or try putting your cutting board in the sink and cutting the onion under cold, running water.
Leaving the onion for minutes in the freezer will definitely reduce your level of irritation while cutting an onion, but it will be a little tougher to cut (owing to the fact that it is partially frozen) and it will be difficult to remove the papery, outermost layer.
Sounds silly, but holding an unlit match (from a matchbook) between your two front teeth while cutting an onion will keep you from tearing up. The theory is, The red end of the match absorbs the sulfuric compounds before they can reach your eyes.Rub Lemon Juice on the Blade of the Knife
An easy fix if you have the ingredient on hand, simply cut a lemon in half and then rub it on the blade of your knife before cutting your onion. Note that, you’ll have to refresh the knife by rubbing the lemon on it after every few cuts of the onion.
Keep a piece of Bread in your mouth
Sounds silly but holding a piece of bread in your mouth while you cut an onion will significantly reduce or eliminate the amount of eye irritation you experience. The theory here is that the bread absorbs the sulfuric compounds before they can reach your eyes.