Onions produce the chemical irritant known as syn-propanethial-S-oxide.
It stimulates the eyes' lachrymal glands so they release tears.
Scientists used to blame the enzyme allinase
for the instability of substances in
a cut onion. Recent studies from
proved that lachrymatory-factor synthase, (a previously undiscovered
enzyme) is the culprit (Imani et al, 2002).
The process goes as follows:
- Lachrymatory-factor synthase is released into the air when we
cut an onion.
- The synthase enzyme converts the amino acids sulfoxides of
the onion into sulfenic acid.
- The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide.
- Syn-propanethial-S-oxide gets into the air and comes in contact
with our eyes. The lachrymal glands become irritated and produces
- National Onion Association
- This Web site provides onion information & tips, recipes, growing
areas, and industry. "The National Onion Association encourages
the United States onion industry to voluntarily exercise all reasonable
efforts to supply consumers with the highest quality, most nutritious,
and safest onions available; and furthermore, to grant appropriate
consideration and respect to the issues of food security, sound pesticide
management, and environmental stewardship."
- NPR Story: Exploring the Stinky Science of Alliums -
July 2, 2010 interview with Eric Block author (and chemist) of Garlic and Other Alliums: The Lore and the Science (2010).
- This site from Texas A&M University provides all types of information
about onions such as planting tips, the varieties, the history and
laws, and onion recipes.
- Why Do Onions Make You Cry -
The short video from the American Chemical Society BytesizeScience YouTube video series illustrates why onions make you cry.
Carolyn and Susan Belsinger. The onion book: a bounty
of culture, cultivation, and cuisine. Loveland, CO,
Interweave Press: c1996. 96 p.
- Block, Eric. The chemistry of garlic and onion. Scientific American, v. 252, March 1985: 114-119.
William H. Crying: the mystery of tears. Minneapolis,
Winston Press, c1985. 175 p.
S. et al. Plant biochemistry: an onion enzyme that makes
the eyes water. Nature, v. 419, Oct. 17, 2002: 685.
Russ. How to read a french fry and other intriguing kitchen
science. Boston, Houghton Mifflin, c2001. p 1-3.
Mara Reid. Onions: a celebration of the onion through
recipes, lore, and history. Reading, MA, Addison-Wesley
Pub., c1995. 193 p.
more print resources...
Search on "onion,"
"lachrymal gland" and "crying" or "tears"
in the Library of Congress Online
The Meat" recipes. Ann Rosener, photographer, 1942. Prints
& Photographs Division, Library of Congress.
According to the Guiness
Book of World Records, the largest onion weighed 10 pounds 14
ounces. It was grown by V. Throup of Silsden, England.
in onion field near Tracy, California. Dorthea Lange, photographer,
. Prints & Photographs
Division, Library of Congress.