Why chopping onions makes you cry

accreditation

Ever wonder why your eyes fill with tears when you chop an onion?

One eye doctor pinpoints the culprit.

Onions use sulphur in the soil to create amino acid sulfoxides, which are sulphur compounds that readily turn into a gas. When an onion is cut, it releases the sulfoxides and enzymes, which react and create a gas called syn-propanethial-S-oxide.

Because onions grow underground, this gas helps deter critters that want to feed on them.

So why do we cry?

But the gas is also what causes your eyes to water when chopping onions, said Dr Robert Rosa Jr., an ophthalmologist at the Texas A&M College of Medicine.

"It really is a complicated chemical process that creates the gas," said Rosa. "They all act as precursors that create the lachrymatory processor – or what makes you tear up."

"Your eyes have a set of nerves that detect anything that's potentially harmful to your eyes. Your eyes react to the gas that is formed, and your eyes try to flush it out with tears," Rosa explained in a school news release.

However, onions pose no serious threat to your visual health.

"Chopping onions can cause some burning and irritation and tears. Other than that, it's pretty safe on your eyes. It's a temporary sensation with no known long-term effects, nor will it worsen any other conditions, like pink eye," Rosa said.

Goggles can prevent the gas from reaching your eyes while cutting onions, but they aren't really necessary, he added.

"Some people may cut the onions in a bowl of water," Rosa said. "I'd personally recommend using eye drops, like comfort drops, to help lubricate or rinse the eyes and dilute the gas exposure to the eyes."

onions, health, facts, infographic


Read more:

Curry, onion guards against cancer

Eye doctors debunk 5 fireworks myths

Green, leafy vegetables may keep glaucoma at bay

We live in a world where facts and fiction get blurred
In times of uncertainty you need journalism you can trust. For 14 free days, you can have access to a world of in-depth analyses, investigative journalism, top opinions and a range of features. Journalism strengthens democracy. Invest in the future today. Thereafter you will be billed R75 per month. You can cancel anytime and if you cancel within 14 days you won't be billed. 
Subscribe to News24
Voting Booth
The ANC's leadership race is heating up. Who do you think will be elected party president at Nasrec in December?
Please select an option Oops! Something went wrong, please try again later.
Results
Nkosazana Dlamini-Zuma has got it in the bag
7% - 507 votes
I foresee a second term for Cyril Ramaphosa
82% - 6222 votes
Don’t discount a Zweli Mkhize win
11% - 814 votes
Vote
Rand - Dollar
17.84
+1.3%
Rand - Pound
20.20
-0.2%
Rand - Euro
17.54
+0.8%
Rand - Aus dollar
11.63
-0.4%
Rand - Yen
0.12
+1.2%
Gold
1,699.36
+2.3%
Silver
20.69
+8.7%
Palladium
2,225.50
+2.7%
Platinum
904.00
+4.6%
Brent Crude
85.14
-2.4%
Top 40
57,850
+0.8%
All Share
64,227
+0.8%
Resource 10
61,646
+2.3%
Industrial 25
77,524
+0.2%
Financial 15
13,816
+0.1%
All JSE data delayed by at least 15 minutes Iress logo
Editorial feedback and complaints

Contact the public editor with feedback for our journalists, complaints, queries or suggestions about articles on News24.

LEARN MORE