Have you ever helped in the kitchen and started crying while cutting an onion?
You may not have been feeling sad at all! The onion was simply playing a tiny chemical trick on your eyes.
But why does an onion make us cry? What happens when we cut it? And why does it sometimes feel like our eyes are under attack?
Let’s grab our imaginary magnifying glasses and investigate the mystery of the crying onion!
What Happens When We Cut an Onion?
An onion may look like a simple vegetable, but inside it are many tiny cells filled with different chemicals.
When an onion is growing underground, these chemicals stay safely separated inside its cells. Everything is peaceful.
Then along comes a knife!
Chop! Chop!
The knife breaks open the onion’s cells. When this happens, some of the chemicals mix together and start a series of chemical reactions.
One of the results is a special, irritating chemical called a lachrymatory factor.
That’s a fancy name, but there’s an easy way to remember it.
“Lachrymatory” comes from a word related to tears!
This chemical can escape into the air as a gas and travel toward your eyes.
Why Do Our Eyes Tear Up?
Your eyes have a clever protection system.
When the onion’s irritating gas reaches your eyes, it reacts with the moist surface of your eyes. Your eyes quickly realize:
“Something is irritating me!”
So they produce tears.
These tears help wash the irritating substance away from the surface of your eyes.
That’s why your eyes start watering when you cut an onion.
Your tears aren’t caused by sadness. They are your body’s way of saying:
“Quick! Wash this away!”
The Onion’s Secret Weapon
Scientists have discovered that onions contain special substances called sulfur compounds.
Sulfur is an element found in many different substances in nature. In onions, sulfur-containing compounds help create the chemicals responsible for that familiar onion smell—and the tears that can follow.
When you cut the onion, an enzyme called alliinase helps start a chemical reaction.
The reaction eventually produces the tear-causing substance that scientists call the lachrymatory factor.
So the whole process looks something like this:
Cut onion → cells break → chemicals mix → irritating gas forms → gas reaches your eyes → your eyes make tears!
Pretty amazing for a vegetable, isn’t it?
Why Do Some Onions Make Us Cry More?
Not every onion makes your eyes water in exactly the same way.
Different onions contain different amounts of the compounds involved in the reaction. The variety of onion, how it was grown, and how fresh it is can all affect how strongly it makes you cry.
That’s why one onion might make you say:
“Oh, that’s not too bad.”
while another makes you reach for a tissue after only a few slices!
Why Does Chopping Faster Sometimes Help?
You may have heard that cutting an onion quickly can help reduce tears.
There is some logic behind this idea, but speed alone isn’t a magic solution.
A sharp knife can help because it tends to make cleaner cuts and crushes fewer onion cells than a dull knife. Fewer damaged cells can mean less mixing of the chemicals that lead to the irritating gas.
So instead of trying to chop as fast as possible, it’s better to use a sharp knife safely—with an adult’s help when needed.
Remember: onions may make you cry, but kitchen knives can cause real injuries!
Does Putting an Onion in the Fridge Help?
You may have heard that chilling an onion before cutting it can reduce tears.
Cooling the onion can slow down some of the chemical reactions involved in producing the irritating compounds. As a result, some people find that a chilled onion bothers their eyes less.
But there is another important point: don’t put a whole onion in the freezer just to stop the tears!
A short time in the refrigerator may be enough if you want to try this trick.
What About Swimming Goggles?
Here’s a funny idea: wear goggles while cutting onions!
Goggles can create a barrier between your eyes and the onion’s irritating chemicals. If the gas can’t easily reach your eyes, your eyes may not react as strongly.
You might look a little silly in the kitchen...
But at least you could chop your onion without crying!
💧 Why Don’t We Cry When We Eat Onions?
Good question!
The tear-causing chemical is produced when the onion’s cells are damaged, especially during cutting.
Once the onion is cooked, heat changes many of its compounds. That’s why cooked onions don’t usually make your eyes water in the same way that freshly cut onions do.
And there’s another bonus:
Cooking onions changes their flavor, making them softer, sweeter, and delicious!
Did You Know?
Here are some fun onion facts!
🧅 Onions are bulbs:
The part we commonly eat grows underground and is a type of modified plant structure called a bulb.
👃 Onions can make your nose react too:
The irritating chemicals can sometimes make your nose feel tingly or cause it to run.
🔥 Cooking changes onions:
Heating onions changes their chemical compounds and makes their strong flavor milder and sweeter.
💦 Tears are helpful:
Your tears don’t just appear when you’re sad. They help keep your eyes clean, moist, and protected.
🔬 A tiny chemical reaction causes a big reaction:
The amount of irritating chemical released by an onion may be tiny, but your eyes are sensitive enough to notice it!