You’re just about ready to chop some veggies and cook some fajitas, but oh wait, not the onions! Onions are common in all sorts of cuisine but feel like they come with a high price to incorporate them into your meal. The price? Tears. Slicing and dicing those crisp veggies causes tears and irritated eyes. Why? Whyyyy?

Just like any living organism, onions come with their own defense mechanism to protect themselves from hungry animals. Their defense mechanism? Propanethial S-oxide, an irritating gas that escapes into the air when an onion is sliced. When this gas encounters moisture, such as the natural moisture around your eyes, it changes into sulfuric acid. Sulfuric acid has a strong smell and irritates your eyes, so to defend themselves your eyes make tears to flush out the fumes. The chemical reaction between the gas and the moisture around your eyes is short-lived, but the lingering gas can cause your eyes to continue to water longer than you’d like.

After this mini science lesson, you may be wondering how to prevent your eyes from watering next time you slice, dice, or chop an onion. Some of these techniques take a bit of prep work, while others call for some extra equipment.

  1. Chill out the onion – Stick your onion in the fridge or freezer before cutting into it. If you choose the fridge, it’s best to keep it in there about 24 hours to cool it to its core.
  2. Cut your onion next to a small fan or range hood – This will blow the gasses away from your face helping your eyes stay tear-free.
  3. Swim goggles – Stop the fumes in their tracks by wearing goggles that seal off the air between your eyes and the onions.
  4. Contact lenses – Wearing contacts while chopping onions may not completely prevent your eyes from watering, but it may delay the tears as there is less surface area exposed for the gas to irritate.

What techniques have you tried to stop the flow of tears while chopping onions? We’d love to try something new. Let us know in the comments.

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