• Question: when you cut onions why do you start to cry

    Asked by to Fiona, Kevin on 26 Jun 2014. This question was also asked by .
    • Photo: Kevin O'Dell

      Kevin O'Dell answered on 26 Jun 2014:

      I confess I googled this one, but I did try to find a reliable website.

      When you cut an onion you break open its cells and as a result certain chemicals that are normally kept apart come together to produce a sulphur-based gas. This wafts up to your eyes (and everywhere else) and when it arrives it reacts with the water/tears in your eyes to make dilute sulphuric acid. This stings your eyes, so you produce more tears to dilute out the sulphuric acid. Which is why you appear to cry.

      Apparently, one way of avoiding this is to put the onion in the fridge before cutting it, as chemical reactions are often slower at cooler temperatures, so this would produce less sulphur-based gas, and fewer tears.

      So I’ve learned something too. Thanks for that!

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