Editing Onion (section)

=== Eye irritation ===

Freshly cut onions can produce a stinging sensation in the eyes of people nearby and often uncontrollable [[tears]]. This is caused by the release of a [[Volatility (chemistry)|volatile liquid]], [[syn-propanethial-S-oxide|''syn''-propanethial-S-oxide]] and its [[aerosol]], which stimulates nerves in the eye. This gas is produced by a chain of reactions which serve as a [[Anti-predator adaptation|defence mechanism]]: chopping an onion causes damage to [[cell (biology)|cells]] which releases [[enzymes]] called [[alliinase]]s. These break down [[amino acid]] [[sulfoxide]]s and generate [[sulfenic acid]]s. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the [[lacrimal gland|lacrimatory]] factor synthase (LFS), producing the ''syn''-propanethial-S-oxide.<ref name="Eric Block 2010" /> This gas diffuses through the air and soon reaches the eyes, where it activates sensory neurons. [[Lacrimal gland]]s produce [[tears]] to dilute and flush out the irritant. Eye irritation can be minimised by cutting onions under running water or submerged in a basin of water.<ref name="Sciam">{{cite web |last=Scott |first=Thomas |title=What is the chemical process that causes my eyes to tear when I peel an onion! |website=Ask the Experts: Chemistry |publisher=Scientific American |url=http://www.sciam.com/article.cfm?id=what-is-the-chemical-proc |access-date=2007-04-28 |archive-date=22 April 2022 |archive-url=https://web.archive.org/web/20220422190206/https://www.scientificamerican.com/article/what-is-the-chemical-proc/ |url-status=live }}</ref> Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb.<ref name=FAQ>{{cite web |url=http://www.onions-usa.org/about/faq.php#cooking |title=FAQ |publisher=National Onion Association |access-date=2013-03-28 |archive-url=https://web.archive.org/web/20110318030002/http://www.onions-usa.org/about/faq.php#cooking |archive-date=18 March 2011 |url-status=dead}}</ref>

<gallery class=center mode=nolines widths=180 heights=180>
File:Cortando cebolla.jpg|Cut onions emit a chemical compound which cause the [[lacrimal gland]]s in the eyes to become irritated, releasing tears.
File:Syn-propanethial-S-oxide-3D-balls.png|Model of [[Syn-propanethial-S-oxide|''syn''-Propanethial-S-oxide]], the volatile molecule that causes eye irritation
</gallery>

The amount of sulfenic acids and lacrimal factor released and the irritation effect differs among ''Allium'' species. In 2008, the [[New Zealand Institute for Crop and Food Research]] created "no tears" onions by [[Genetically modified organism|genetic modification]] to prevent the synthesis of lachrymatory factor synthase in onions.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2008/02/080202115345.htm |title=Tearless Onion Created in Lab Using Gene Silencing |website=ScienceDaily |date=5 February 2008 |access-date=23 November 2016 |archive-date=24 November 2016 |archive-url=https://web.archive.org/web/20161124025149/https://www.sciencedaily.com/releases/2008/02/080202115345.htm |url-status=live }}</ref> One study suggests that consumers prefer the flavour of onions with lower LFS content.<ref>{{Cite journal |last1=Kim |first1=Ha-Yeon |last2=Jackson |first2=Daniel |last3=Adhikari |first3=Koushik |last4=Riner |first4=Cliff |last5=Sanchez-Brambila |first5=Gabriela |date=2017-10-01 |title=Relationship Between Consumer Acceptability and Pungency-Related Flavor Compounds of Vidalia Onions |journal=Journal of Food Science |volume=82 |issue=10 |pages=2396–2402 |doi=10.1111/1750-3841.13915 |pmid=28898424}}</ref> Since the process impedes sulfur ingestion by the plant, some find LFS− onions inferior in flavour.<ref>{{Cite journal |last1=Eady |first1=Colin C. |last2=Kamoi |first2=Takahiro |last3=Kato |first3=Masahiro |last4=Porter |first4=Noel G. |last5=Davis |first5=Sheree |last6=Shaw |first6=Martin |last7=Kamoi |first7=Akiko |last8=Imai |first8=Shinsuke |date=2008-08-01 |title=Silencing Onion Lachrymatory Factor Synthase Causes a Significant Change in the Sulfur Secondary Metabolite Profile |journal=Plant Physiology |volume=147 |issue=4 |pages=2096–2106 |doi=10.1104/pp.108.123273 |pmid=18583530 |pmc=2492635}}</ref>

A method for efficiently differentiating LFS− and LFS+ onions has been developed based on [[mass spectrometry]], with potential application in high-volume production;<ref>{{Cite journal |last1=Joyce |first1=Nigel I. |last2=Eady |first2=Colin C. |last3=Silcock |first3=Patrick |last4=Perry |first4=Nigel B. |last5=van Klink |first5=John W. |date=January 2013 |title=Fast Phenotyping of LFS-Silenced (Tearless) Onions by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) |journal=Journal of Agricultural and Food Chemistry |volume=61 |issue=7 |pages=1449–1456 |doi=10.1021/jf304444s |pmid=23350988|bibcode=2013JAFC...61.1449J }}</ref> [[gas chromatography]] is also used to measure lachrymatory factor in onions.<ref>{{Cite journal |last1=Tewari |first1=Gyanendra M. |last2=Bandyopadhyay |first2=Chiranjib. |date=1975-07-01 |title=Quantitative evaluation of lachrymatory factor in onion by thin-layer chromatography |journal=Journal of Agricultural and Food Chemistry |volume=23 |issue=4 |pages=645–647 |doi=10.1021/jf60200a0441|doi-broken-date=1 November 2024 }}</ref><ref>{{Cite journal |last1=Schmidt |first1=Norman E. |last2=Santiago |first2=Leanne M. |last3=Eason |first3=H. Donald |last4=Dafford |first4=Kurtus A. |last5=Grooms |first5=Chris A. |last6=Link |first6=Tammy E. |last7=Manning |first7=Dana T. |last8=Cooper |first8=Sylina D. |last9=Keith |first9=R. Chad |date=1996-01-01 |title=Rapid Extraction Method of Quantitating the Lachrymatory Factor of Onion Using Gas Chromatography |journal=Journal of Agricultural and Food Chemistry |volume=44 |issue=9 |pages=2690–2693 |doi=10.1021/jf950686s|bibcode=1996JAFC...44.2690S }}</ref> In early 2018, [[Bayer]] released the first crop yield of commercially available LFS-silenced onions under the name "Sunions".<ref name=":0">{{Cite news |url=https://www.npr.org/sections/thesalt/2018/02/08/583703262/stop-crying-tear-free-onions-are-here |title=Stop Crying! Tear-Free Onions Are Here |last=Danovich |first=Tove |date=8 February 2018 |publisher=NPR |access-date=13 April 2018 |archive-date=17 April 2018 |archive-url=https://web.archive.org/web/20180417025118/https://www.npr.org/sections/thesalt/2018/02/08/583703262/stop-crying-tear-free-onions-are-here |url-status=live }}</ref> They were the product of 30 years of cross-breeding; genetic modification was not employed.<ref name=":0" /><ref>{{Cite news |url=http://www.latimes.com/food/sns-dailymeal-1863539-healthy-eating-tearless-onions-121917-20171219-story.html |title=Onions that don't make you cry are finally here |last=Van Hare |first=Holly |date=19 December 2017 |newspaper=Los Angeles Times |access-date=15 April 2018 |archive-date=13 April 2018 |archive-url=https://web.archive.org/web/20180413034721/http://www.latimes.com/food/sns-dailymeal-1863539-healthy-eating-tearless-onions-121917-20171219-story.html |url-status=live }}</ref>

[[Petiveria|Guinea hen weed]] and [[Allium siculum|honey garlic]] contain a similar lachrymatory factor.<ref>{{Cite news |url=https://www.nytimes.com/2017/09/05/science/onions-crying-chemicals.html |title=Why Onions Make You Cry |last=Klein |first=Joanna |date=5 September 2017 |work=The New York Times |access-date=16 April 2018 |archive-date=17 April 2018 |archive-url=https://web.archive.org/web/20180417025055/https://www.nytimes.com/2017/09/05/science/onions-crying-chemicals.html |url-status=live }}</ref> Synthetic onion lachrymatory factor has been used in a study related to tear production,<ref>{{cite journal |doi=10.1007/s10384-009-0786-0 |volume=54 |title=Using synthesized onion lachrymatory factor to measure age-related decreases in reflex-tear secretion and ocular-surface sensation |year=2010 |journal=Japanese Journal of Ophthalmology |pages=215–220 |last1=Higashihara |first1=Hisayo |last2=Yokoi |first2=Norihiko |last3=Aoyagi |first3=Morihiro |last4=Tsuge |first4=Nobuaki |last5=Imai |first5=Shinsuke |last6=Kinoshita |first6=Shigeru |s2cid=23549173 |issue=3 |pmid=20577855}}</ref> and has been proposed as a nonlethal deterrent against thieves and intruders.<ref>{{Cite patent |country=US |number=9482496B1 |status=patent |title=Wall-mounted nonlethal device for defending against intruders |pubdate=2015-06-01 |gdate=2016-11-01 |pridate=2015-06-01 |inventor=James Anthony Rocchi, Thomas John Stewart |invent1=James Anthony Rocchi |invent2=Thomas John Stewart |assign1=Fighting Chance Systems Inc |url=https://patents.google.com/patent/US9482496B1/en }} {{Webarchive|url=https://web.archive.org/web/20210318041651/https://patents.google.com/patent/US9482496B1/en |date=18 March 2021 }}</ref><ref>{{cite patent |country=US |number=9890561B2 |status=patent |title=Pressurized chemical theft deterrent device |pubdate=2017-03-03 |gdate=2018-02-13 |pridate=2016-03-04 |inventor=Yves Perrenoud, Daniel Idzkowski |invent1=Yves Perrenoud |invent2=Daniel Idzkowski |assign1=Skunklock Inc |url=https://patents.google.com/patent/US9890561B2/en }} {{Webarchive|url=https://web.archive.org/web/20200113141617/https://patents.google.com/patent/US9890561B2/en |date=13 January 2020 }}</ref>

Onions are toxic to animals including dogs, cats, and [[guinea pig]]s.<ref name="Cope2005">{{cite journal |last1=Cope |first1=R.B. |last2=Monteiro |first2=L.N. |last3=Rocha |first3=N.S. |title=''Allium'' species poisoning in dogs and cats |journal=Veterinary Medicine |date=August 2005 |volume=100 |issue=8 |pages=562–566 |url=https://www.aspcapro.org/sites/default/files/c-vetm0805_562-566.pdf |access-date=22 July 2022 }}</ref><ref name="Salgado2011">{{cite journal |last=Salgado |first=B.S. |title=''Allium'' species poisoning in dogs and cats |journal=Journal of Venomous Animals and Toxins Including Tropical Diseases |year=2011 |volume=17 |issue=1 |pages=4–11 |doi=10.1590/S1678-91992011000100002 |doi-access=free |hdl=11449/12942 |hdl-access=free }}</ref>