Things You'll Need
Cutting into an onion with a knife releases enzymes in vapor form. When the vapor reaches your eyes, it turns into a form of sulfuric acid, causing irritation. The eyes then try to dilute the volatile gas with tears. To avoid crying as you prepare your recipes, you'll need to find effective ways to stop the vapor from reaching your eyes.
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Chill your onions. Placing an onion in a very cold refrigerator or freezer until it's chilled will keep the enzymes from activating while you cut.
Use a sharp knife. Dull knives damage more plant cells, leading to an increased amount of vapor being released into the air.
Cut the onion under water. This will stop all irritating vapors because the gas, like any acid, will dissolve into water. You can also cut the onion under running water.
Use ventilation. A fan generating an air current away from your eyes will blow away the tear gas.
Place a piece of bread in your mouth so that half of it sticks out. This will help absorb the offending vapors.
Combine different approaches for greater protection when cutting onions.
Use caution when handling sharp knives.