The act of cutting an onion itself is what causes it to sting your eyes: the chemical responsible is called propanethial S-oxide, and is released when certain cells inside the onion are exposed to the air. It wafts towards your eyes and reacts with the water there to form sulphuric acid, causing a burning sensation and making your eyes water in order to flush it out. Luckily, there are a few things you can do to make it less unpleasant.
- Placing the onions in the fridge for a few hours before chopping can reduce the strength of the irritation.
- Use a properly sharpened knife. This will cause less damage to cell walls and fewer irritants will be released.
- Keep the exposed cuts away from you. As soon as you cut an onion in half, turn both halves down on your cutting board. Leave the side you aren’t currently chopping unpeeled. Once you’ve finished one half, move the chopped onion into a prep bowl and set it on the opposite side of the kitchen before proceeding with the remaining onion.
- Position your cutting board next to the stove and turn on the exhaust fan, pulling some of the chemical irritants away.
- If you have contact lenses, wearing them instead of glasses while chopping the onions can make a world of difference.
- If it’s really bothering you, have a look online – you can buy special onion goggles (or use swimming goggles to be extra fashion-forward)!