Fun Science Facts from the Library of Congress
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Question Why does chopping an onion make you cry?Answer
Unstable chemicals.
Camp Kearny, Cal. “Anti-onion” gas mask. Between 1917-1919. Prints & Photographs Division, Library of Congress.
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 Japan, however, proved that lachrymatory-factor synthase, (a previously undiscovered enzyme) is the culprit (Imai et al, 2002).
Maule’s seed catalogue for 1891 by Wm. Henry Maule (Firm). Henry G. Gilbert Nursery and Seed Trade Catalog Collection (on the Internet Archive), National Agricultural Library.
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-Propanethial-S-oxide.
Syn-Propanethial-S-oxide gets into the air and comes in contact with our eyes. The lachrymal glands become irritated and produces the tears!
Pungent red onions. Agricultural Research Service, U.S. Department of Agriculture.
Published: 11/19/2019. Last Updated: 12/15/2021. Author: Science Reference Section, Library of Congress
Related Websites
Cooking Onions Without Crying
External
(University of Nebraska-Lincoln Extension)
National Onion Association
External
- This website 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."
Exploring the Stinky Science of Alliums
External
(NPR, July 2, 2010) - Interview with Eric Block author (and chemist) of Garlic and Other Alliums: The Lore and the Science .
Onions
External
(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?
External
(PennState Extension)
Further Reading
Dille, 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, Mar. 1985: 114-119.
Frey, William H. Crying: the mystery of tears . Minneapolis, Winston Press, c1985. 175 p.
Imai, S., et al. "Plant biochemistry: an onion enzyme that makes the eyes water." Nature , v. 419, Oct. 17, 2002: 685.
Parsons, Russ. How to read a french fry and other intriguing kitchen science . Boston, Houghton Mifflin, c2001. p. 1-3.
Rogers, Mara Reid. Onions: a celebration of the onion through recipes, lore, and history . Reading, MA, Addison-Wesley Pub., c1995. 193 p.
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