Freshly Baked Science

onions on a chopping board cut into rings crying pink accent colour black and white with colour

Holding Back The Tears

5th September 2018

I think it’s safe to say that we have all been personally victimised by an onion at some point in our lives. There you are, just innocently preparing a delicious dinner, when suddenly, your eyes become a burning, streaming and stinging mess, just moments after cutting into an onion.


*Top tip: from personal experience, don’t use your onion covered hands to wipe your eyes at this point… it is only going to make matters a whole lot worse…*


So what actually makes onions the bullies of the kitchen and more importantly, is there a way to stop them getting to you?!


The reason onions make us cry is part of their survival technique. The horrible teary response we get when we are near a cut onion is from a gas they release to help protect them from attack.


When you slice into an onion, you start off a chain of chemical reactions, much like pushing over a domino. Firstly, the cells inside the onion are broken up, which releases an enzyme (a substance which can break down or build up a molecule). This enzyme breaks chemicals down into flavour molecules, which is what gives an onion its taste.


The flavour molecules aren’t, however, the culprits of the tears. There are other chemicals in this reaction which are turned into an oniony tear gas by another enzyme. When this tear gas comes into contact with the front of the eye, a signal is sent to the brain, telling it that an irritant has arrived. The brain then sends a new signal to tear gland, telling it to produce tears. A mixture of tears and blinking is the body’s response mechanism to get rid of the irritant.


So now we know why it happens, how about how to stop it?


Tip 1: Freeze the onion


How it works: The cold should slow down the enzymes, so the tear gas is produced at a much slower rate, if at all.


Pros: No Tears


Cons: Harder to slice and may give you frostbite…


Tip 2: Use a sharp knife *caution advised*


How it works: The sharper the knife, the less damage to the cell walls and therefore less tear gas released.


Pros: Slightly less burning and tears


Cons: Puts you at higher risk of chopping your fingers off and still some tears…


Tip 3: Put a slice of bread in your mouth


How it works: The airy texture of the slice of bread will absorb the gases, stopping them from reaching your eyes.


Pros: No tears and a delicious snack while you cook your dinner!


Cons: Absolutely none… unless you’re gluten intolerant, of course.


Tip 4: Wear swimming goggles


How it works: Just like they stop water from getting in your eyes in the pool, they will also stop the gases from getting in your eyes.


Pros: No tears


Cons: Fashionably questionable


I hope your next onion chopping adventure is slightly more comfortable with these tips! Share with your friends and family to save them from the devilish onion gas! Be sure to send us a selfie of you trying out one of these techniques (twitter: @magazinewonk, Instagram: @wonkscience, email: for a chance to be featured on our social media!

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