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How Onions ACTUALLY Make You Cry (And How to Stop Them)
How Onions ACTUALLY Make You Cry (And How to Stop Them)
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0:00
Onions. We love to hate them.
0:02
Or rather, our eyes hate that we love them so much.
0:05
They are one of the oldest recorded vegetables in continuous use,
0:08
with records dating back 4,000 years,
0:11
and they’ve made their way into pretty much every culinary tradition in the world.
0:15
As amazing as they are, they’ve got one really annoying flaw: all of the crying.
0:20
Every time you cut into one, you can’t help but
0:22
well up like you’re watching a sad dog movie.
0:25
We actually know quite a lot about what’s happening
0:27
at the chemical and biological levels to make this reaction happen.
0:31
But a study published in October 2025 looks at the onion-crying problem
0:35
from a new perspective: physics.
0:38
They examined the droplets flung out of an onion
0:41
being cut in various ways with a precisely-tuned onion guillotine.
0:46
And the results show us there is still more to learn about how onions make us cry.
0:52
[♪ INTRO]
0:56
Now before we dive into the French Revolution of onions, let’s recap the science
1:00
behind the onion’s uncanny ability to bring tears to even the toughest eyes.
1:04
There’s a chemical that gets released when you cut into an onion
1:07
called syn-propanethial-S-oxide which causes the glands in your eye
1:12
that produce tears to work overtime to attempt to flush the irritant of your eyes.
1:17
The weird thing is, onions don’t contain any propanethial-S-oxide.
1:21
Instead, they contain the ingredients for it.
1:24
First, when you cut into the onion, your knife breaks open a lot of cell walls.
1:28
And this is all the onion needs to introduce the enzyme
1:30
alliinase to air and produce 1-propenesulfenic acid.
1:34
That chemical then reacts further with another enzyme
1:37
to make the tear-inducing propanethial-S-oxide.
1:40
Given how long we’ve been tearing up at onions,
1:43
you might be surprised at how recent some of this science is.
1:46
We only discovered that second step, where 1-propenesulfenic acid reacts
1:50
to another enzyme to make the actual tear-jerker substance, in 2002.
1:55
Which, to me, is like 5 years ago.
1:58
So that’s the chemistry behind the effect.
2:00
A weird side-note: onions get their sulfur from the soil,
2:03
and acid rain contains a lot of sulfur.
2:06
So a strange consequence of the success of tackling acid rain
2:09
in many urban areas is that it might actually make onions milder!
2:13
It feels like it was worse when I was a kid.
2:15
Maybe I’m just stronger now.
2:16
This molecule is also pretty much unstoppable once it gets to your eyes,
2:20
so the only way to truly avoid tearing up is to
2:22
prevent it from reaching your eyes in the first place.
2:25
So the chemistry and biology are pretty much solved.
2:28
But what hasn’t been addressed yet is the physics.
2:30
As in, we don’t know exactly how this substance
2:33
travels to your eyes in order to be able to stop it.
2:36
Enter: the onion guillotine, courtesy of a research group at Cornell University.
2:40
They also employed high-speed cameras and an electron microscope
2:44
to test which configurations of knife sharpness, angle and speed of cutting,
2:49
and temperature of onion resulted in the worst onion-juice splashes.
2:53
They found that the chemical is carried in droplets,
2:56
released in an initial burst when a blade first punctures the onion’s surface,
3:01
then more slowly as the blade travels through.
3:03
In their tests, a more blunt blade applied more pressure
3:07
to the membrane before breaking it, causing a bigger burst of droplets.
3:11
And that reinforces the wisdom that you should
3:12
always use a sharp knife in the kitchen.
3:14
Keeping blades sharp also reduces the chance of injuring yourself
3:18
(which seems a little counterintuitive, but it reduces the amount of pressure
3:22
you need and the chance of the knife slipping).
3:24
But this is another, brand new reason!
3:26
The Cornell team also found that cutting faster caused
3:29
more droplets to be released, so a cautious approach
3:32
with a sharp knife might be the best way to minimize tear production.
3:36
As for the common “hack” of putting your onions in the fridge to somehow
3:40
limit their ability to hurt your tear ducts’ feelings,
3:42
the researchers did not find any support for this.
3:46
In fact, chilled onions released more droplets in their experiments.
3:50
They thought that this might be because the onion tissues get stiffer when cold,
3:54
causing them to absorb more of the knife’s pressure before breaking,
3:57
then bursting with even more energy.
4:00
There’s another solution running around out there,
4:02
which is that you should put a damp towel
4:04
or bowl of water near where you’re cutting.
4:07
Given that the offending chemical is water-soluble,
4:10
if you could somehow get the onion droplets
4:12
to hit the water before it hits your eyes, that seems like it could work.
4:15
It wasn’t part of the experiments in this paper,
4:17
but if I’m allowed to make requests, it might make for a good follow-up!
4:21
Our speculation, though, is that the Cornell’s team’s experiments
4:24
show the droplets flying upwards,
4:26
so water on the worktop can only work to mop up splashes and bounces,
4:31
and wouldn’t be in a position to stop that first attack on your eyeballs.
4:34
Outside of just stopping a common kitchen annoyance,
4:37
this research has implications for food safety in general.
4:41
Droplets sprayed from vegetables don’t only carry tear-inducing chemicals,
4:45
but also potentially foodborne pathogens as well.
4:48
So, this research suggests that a sharper knife keeps your kitchen safe
4:51
in yet another way, by preventing potential pathogens from being spread around.
4:56
Armed with the knowledge from an onion guillotine
4:58
and some fancy imaging equipment, we can at least help you out
5:02
if you really can’t stand that stinging feeling in your eyes.
5:05
The best way to limit the amount of onion droplets spraying into your eyes
5:09
seems to be to keep your knife sharp and to cut slowly.
5:13
Short of investing in goggles, anyway.
5:15
Which I have heard from prep cooks, is something they do.
5:17
And wildly, that strategy might also keep your whole kitchen safer at the same time.
5:23
[♪ OUTRO]
How Onions ACTUALLY Make You Cry (And How to Stop Them) - Video học tiếng Anh
