Why Onions Make You Cry (and how to avoid it!)

Nobody likes to cut onions because they seem to fight back!  Only a few seconds after chopping into them, your eyes start burning and tearing up so that it’s hard to concentrate and finish the job.  What exactly is invoking all this drama?  

It turns out that onions are equipped with a self-defense mechanism to make them unpalatable to predators, underground and above-ground.  When an onion is sliced or broken open, sulfoxides and onion enzymes are emitted in the form of sulfenic acid.  When the acid and onion enzymes react together, they create syn-propanethial-S-oxide gas. That gas wafts up to your eyes, reacts with the water naturally covering your eyes, and generates sulfuric acid and other irritating substances that can induce tears.  (Why Onions Make You Cry, and How to Prevent This Teary Reaction)

There are A LOT of home remedies on the internet to keep you from tearing up while cutting onions.  According to FoodandWine.com, they are mostly useless…unless you’re playing a prank on your friend by making them look silly while cutting the onions for you!  Here are their suggestions to avoid onion drama:

  • Sharpen your knife well before cutting.  This helps “slice” the onion instead of “bruising” it with a dull blade, because crushing the cells causes more acid and enzyme to react.

  • Briefly (for 30 minutes) freeze the onions before cutting, which will reduce cell “trauma” and cause resulting gases to be cooler, so that they tend to stay on the level of the cutting board and not rise to your face.  Alternatively, you can place the onion in a bowl of ice water.

  • Protect your eyes: you can use any type of clear full-face mask, onion goggles, or large sunglasses to deflect the gases away from your eyes (this works!)

  • Add a splash of citrus juice or vinegar to alter the pH enough to hamper the enzyme’s ability to function as usual.

Finally, here are the best tips from our own staff: 

  • I cut the onions next to my stove with the exhaust vent on full power.  If I can keep them at arm’s length with the onions closest to the vent, the fumes don’t have a chance to go to my eyes!

  • “Penny’s tip”: take a paper towel and dampen it with water, halfway wring it out and place it next to the onions while you cut them.  The water in the paper towel absorbs the gas and mostly prevents it from reaching your eyes.  The onion smell is detectable, but no tears!

Photo by vivek sharma on Unsplash