How do we know?
↻ One of the pages with a moving picture
A team in Japan found that it takes two steps.
- A whole onion has no stinging chemical. Cutting breaks its cells so kept-apart chemicals mix, like in a glow stick.
- Two enzymes work one after the other to make a stinging gas, propanethial-S-oxide.
- The gas floats up and meets the water on your eye, making an acid that stings.
- Your eye makes tears to wash the stinging stuff away.
People thought one enzyme made the gas. In 2002 a team in Japan showed in the journal Nature that it takes two steps.
Scientists have even grown a “tearless” onion. Turning off the second enzyme made an onion that didn’t sting eyes.
Onions grown in soil with more sulfur taste hotter. Vidalia onions from Georgia taste sweet because the sandy soil there is low in sulfur.
Wow number
2002 In 2002 scientists in Japan found the second enzyme that makes onion tears!
Myth or fact?
The stinging chemical is always inside onions. Myth. It is only made when the onion’s cells are broken.
Scientists have grown a “tearless” onion. Fact. Turning off the second enzyme made an onion that didn’t sting eyes.
Think about it
Onions grown in soil with more sulfur taste hotter. Why might that be?
Where in the world?
Vidalia, Georgia, USA where Vidalia onions are Georgia’s official vegetable. They taste sweet because the sandy soil there is low in sulfur — 32.2177° N, 82.4135° W.
Where these facts come from
Every number on page 84, and who measured it
This page tells us about the stinging gas an onion makes when you cut it.
Propanethial-S-oxide — The Royal Society of Chemistry, a big group of chemists in the UK
edu.rsc.org/magnificent-molecules/propanethial-s-oxide/3010038.article
We checked it on 31 October 2026
This page is the 2002 science paper about the onion's tear-making enzyme.
An onion enzyme that makes the eyes water — Nature, a famous science journal
nature.com/articles/419685a
We checked it on 31 October 2026
This page tells us about a "tearless" onion made in a lab.
Enzyme That Makes You Cry–Crystal Structure of Lachrymatory Factor Synthase from Allium cepa — A science paper about the onion enzyme that makes you cry, shared by the U.S. National Library of Medicine
pmc.ncbi.nlm.nih.gov/articles/PMC5693239
We checked it on 31 October 2026
This page tells us why Vidalia onions from Georgia taste sweet.
Soil conditions, fertilizers affect the sweetness of Vidalia onions — The University of Georgia's farming college
fieldreport.caes.uga.edu/soil-conditions-fertilizers-affect-the-sweetness-of-vidalia-onions
We checked it on 31 October 2026
Has this changed?
Yes, this one changed in 2002, when scientists found that onions need two enzymes, not one.
It could change again as scientists learn more about the tearless onion.
Words from this page
- enzyme
- A natural chemical that helps change one thing into another.
- sulfur
- A yellow chemical found in soil that makes onions taste hotter.
Try it!
Wash away a “sting” with “tears”.
1. Put a drop of food coloring on a white plate: the “sting”. 2. With a dropper, add water drops next to it and tilt the plate. 3. Count how many “tears” it takes to wash the color away.
What happens: the water thins the color and carries it off, like tears.
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