Why Do Onions Make You Cry?

(Last Updated On: December 10, 2018)

Why Do Onions Make You Cry?
We’ve all faced the problem before. Salads, pastas, and stir frys, among other dishes, have left us in tears. Not from their delicious flavor, but from chopping the onions. This can be distracting and even dangerous, as there are lots of ways to hurt yourself in the kitchen.

It’s a well-known fact that chopping onions can make you cry, but why is this the case? Why do onions make you cry?

Why Do Onions Make You Cry? The Science Behind It

Onions are pretty tough vegetables. You can pick, peel, and boil them with no consequences whatsoever. However, as soon as your knife pierces the onion, it begins a chemical reaction. When the onions cells break open, it mixes chemicals within the vegetable that were originally separated. The result of this is a chemical called propenal S-oxide, also known as lachrymatory factor (LF), which causes people to cry.

When LF particles make their way into the front of your eye (aka your cornea), it attacks your sensory nerves in a way similar to tear gas! When onion cells break open, they also release an enzyme called allinase, which breaks down into flavor molecules (also giving onions their own signature taste).

Your body’s natural defense is to blink while your tear ducts open up, releasing tears. This is your body’s way of cleaning the LF off of your eye. Ironically, LF is the onions natural defense mechanism – It is meant to protect it from microbes, animals and humans.

Avoiding the Tears

Now that we know a little bit more about why onions make us cry, let’s figure out a few ways to avoid it.

Using a Sharp Knife

LF is released when the cells of the onion are broken open. Using a dull blade will crush the onion, which will open more cells. If you use a sharper blade it will make a cleaner cut in the onion, making it harder to release LF. Give your knife a quick sharpen and see for yourself.

Cutting Under Water

This one is a classic. Cutting onions in a bowl of water doesn’t allow the LF to become airborne. Instead of getting in your eyes, it goes directly into the water. However, be careful if you use this method, as the water can make the onion extremely slippery. Be sure to have a firm grip when cutting under water. It also helps if you use a sharp knife.

Wearing Airtight Goggles

You may not want to do this if you’re cooking in front of your date, however this one is effective. Wearing airtight goggles creates a protective layer between your cornea and the LF. As the LF becomes airborne, it hits the lens of the goggles, keeping your eyes tear free. Be warned, regular eye glasses do not work, as they don’t create an airtight seal.

Cutting Next to a Fan

If you place a fan next to you while cutting onions, it blows the airborne LF away from your eyes. Use a small fan or a low speed while doing this, as it might send pieces of onion flying across the kitchen.

Freezing/Chilling the Onion

If you have some time to kill before prepping for dinner, try chilling the onion in the fridge or freezer. Cooling the onion down minimizes the amount of airborne LF the onion can produce. It also has no effect on the flavor. If you’re using the freezer, throw it in for 10 to 15 minutes. If you’re using the fridge, wait a little longer at 15 to 20 minutes. However, if you’re going to use the fridge, don’t forget about it, as it can leave your fridge smelling like onions.

So there you have it. Sometimes it’s OK to have a good cry, but it doesn’t have to be while you’re making dinner.

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