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Surgeon David Allamby FRCS(Ed), FRCOphth
 David Allamby

SCROLL DOWN one vegetable reduces us all to tears

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We are known to cry at all sorts of things, from breakups, to puppies, and even the occasional soap episode or two. But there is one thing that makes us cry without fail. That's right, onions.

But why does this seemingly harmless vegetable leave us balling our eyes out?

Onions are a staple ingredient and key source of flavour in many meals across the globe.

With this in mind then, many of us are likely to have experienced the lethal power of this not-so-innocent vegetable that brings us to tears to the point we sometimes have to stop to take a break, mid chopping session.

For years we have accepted the effects onions have on our eyes whilst we cut them up, but have you ever wondered what it is about this vegetable that turns on the waterworks?

crying from onionsWhy do onions make us cry?

Onions make us tear up because of a reaction in the vegetable that occurs as we break into it, which causes the release of a chemical called lachrymatory factor (LF), which then irritates our eyes. Consider yourself safe when you’re washing or peeling the onion. It is not until it is cut open that this chemical is released, as the onion’s cells break open allowing for two normally separate substances to mix.

Once combined, they produce the tear jerking chemical we are all too familiar with.

Onion’s have a self-defence mechanism too you know...

Interestingly, there is method to the madness on why onions produce the potent chemical that brings us to tears, and it all boils down to evolution and defence mechanisms. Here is what happens to the onion as it grows:

  • growing onionsAll onions are grown underground, where the vegetable faces a world of critters looking for food. With this threat, the onion has evolved to produce a way to protect itself from being eaten
  • As onions grow underground they mix with the sulphur in the dirt that then created amino acid sulfoxides. These are essentially sulphur compounds that can readily be turned into a gas
  • When an onion is broken apart, or attacked by one of these critters for example, the sulfoxides and onion enzymes are released and become combined, which as a result creates a sulfenic acid
  • This acid then reacts with the onion enzymes to produce the gas we all know and hate, as it floats up to the chopped (or bitten) area, in the hope of stopping critters from going any further

tear productionWhy do we cry in reaction to this gas?

Just like the onion produces this potent gas as its own defence mechanism, our eyes do the same by producing tears. It is essentially a set of nerves in our eyes detecting a potentially harmful gas, which as a result sees our eyes try to flush it away with tears. Pretty clever, right?

Are some onions worse than others? 

Definitely! According to Science Daily, white, yellow and red onions all have a higher concentration of the onion enzymes that are necessary to produce this eye watering gas, whereas sweet onions, green onions and scallions have fewer of these enzymes!

Avoid the tears

If the tears are too much you can try the following suggestions to reduce the waterworks as you’re chopping:

  • Wear protective goggles - this will prevent the gas from reacting with your eyes. If you don’t mind looking like a scientist more than a chef this is definitely an option to consider!onion goggles
  • Use eye drops - the extra moisture will dilute the gas exposure to your eyes
  • Freeze the onion or soak it in cold water - the cold temperature will slow down the production of the eye-stinging gas!

Although having irritated teary eyes when making your dinner is not ideal, it is of no harm either, with no long-term effects known. Onions are great for your health. From improving your sleep to lowering high cholesterol, they are definitely not worth removing from your diet!


So grab some tissues and get chopping!

happy onion


National Onion Association

Science Daily

The New York Times

Read more for posts on eye health, laser eye surgery, and vision, here

By: David
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