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Why do onions make you cry

October 16, 2018

It’s a scenario you’ve doubtless experienced time and again. Whether you’re preparing a meal solo or stepping in as a dutiful sous chef, you know if you find yourself chopping an onion, you’ll end up in tears, likely sooner than later. Of course, onions themselves don’t typically bring on a wave of emotion on their own – it’s the unavoidable irritation they cause to your eyes.

So why does chopping an onion bring us to tears?

Unless you’re cooking with a broken heart, your reaction is purely chemical. Slicing into an onion breaks its cells, causing it to release a tear-jerking chemical compound called lachrymatory factor (LF). Upon reaching your eyeballs, LF activates the nerve endings in your cornea and tear ducts, causing a protective tearful reaction. Essentially, that’s a scientific way of saying the chemicals onions release when chopped send your eyes into defense mode.

“Your eyes have a set of nerves that detect anything that’s potentially harmful to your eyes,” said Robert H. Rosa Jr., MD, ophthalmologist and professor of surgery and medical physiology at the Texas A&M College of Medicine. “Your eyes react to the gas that is formed, and your eyes try to flush it out with tears.”

Perhaps ironically, LF evolved as a defense mechanism to protect onions against anyone trying to chop, caramelize or otherwise consume them, but Americans have decided it’s worth it to power through the tears, each consuming a staggering average of 20 pounds of onion per year.

Despite discovering why we react to onions the way we do, there’s still a lot we don’t know about the ins and outs of how onions affect our eyes. Some people have a stronger reaction to onions than others. Some types of onions don’t cause as strong of a reaction in some people. According to Dr. Marcin Golczak, a biochemist at Case Western Reserve, it all could depend on the onion’s freshness, how much LF it produces or a mutation that could alter LF’s activity. Regardless, the gas from an onion really isn’t dangerous, though it might cause some pain and frustration.

“Chopping onions can cause some burning and irritation and tears,” said Rosa. “Other than that, it’s pretty safe on your eyes. It’s a temporary sensation with no known long-term effects, nor will it worsen any other conditions, like pink eye.”

So is there a way to skip the tears without skipping onions altogether? It’s possible. Japanese scientists are working to develop a “tearless” onion, but are getting mixed results. Apparently, the onion’s signature taste is hard to achieve in an LF-free version.

For now, it looks like we’re stuck with crying it out in the kitchen. However, there are a few approaches you can try to next time you’re chopping an onion:

  1. Keep a bottle of eye drops in your kitchen. You can use them to rinse and lubricate your eyes as you cut and dilute the gas exposure to your eyes.
  2. Cool it down. Put your onion in the fridge for a bit before you chop it, or submerge the onion in water while you chop it. Either way reduces the onion’s temperature, slowing down the chemical reaction and resulting in less LF. However, this can also mess with the onion’s natural flavor.
  3. Grab some goggles. This is the only surefire way to stay tear free while chopping onions!  

At the end of the day, you might have to cry a little to get the best flavor from your onion!

If you find your eyes watering all the time and you’re NOT cutting an onion, then you need to call your friends at OCLI. Dr. Silverman and his team are ready to assist you with any of your eye care needs!

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