Lye

2025-08-17T18:16:29Z

2A00:23C6:ADAD:5E01:E045:FB0F:B137:59A7: /* Food */

{{Short description|Sodium hydroxide and potassium hydroxide}}
{{Other uses}}
[[File:HK TKO 將軍澳廣場 Tseung Kwan O Plaza mall shop JHC 日本城 Japan Home Centre goods June 2019 SSG 02.jpg|thumb|Lye for sale in a shop in Hong Kong]]
'''Lye''' is the common name of various [[alkaline]] solutions, including '''soda lye''' (a solution of [[sodium hydroxide]]) and '''potash lye''' (a solution of [[potassium hydroxide]]).<ref>{{cite web|title=Lye|work=Merriam-Webster.com|url=https://www.merriam-webster.com/dictionary/lye|access-date=15 June 2025}}</ref><ref>{{cite book|last1=Matson|first1=Michael L.|last2=Orbaek|first2=Alvin W.|title=Inorganic Chemistry For Dummies|year=2013|location=Hoboken|publisher=John Wiley & Sons|isbn=978-1-118-21794-8|page=333|url=https://archive.org/details/inorganicchemist0000mats/page/333}}</ref> Lyes are used as cleaning products, as ingredients in soapmaking, and in various other contexts.

==History==
The word {{wikt-lang|en|lye}} derives from the root *''lau'', meaning to wash (compare {{wikt-lang|en|lave}}, {{wikt-lang|en|lather}}) and has [[cognates]] in all the [[Germanic languages]].<ref>{{Cite OED|lye|1176932237|access-date=15 June 2025}}</ref> Traditionally, lye was made by leaching [[wood ash]]es in water, creating an alkaline liquor rich in [[potassium carbonate]] or potash. The alkalinity could be increased by adding [[slaked lime]], which would cause the solute to become potassium hydroxide or caustic potash.<ref>{{cite book|last=Clarke|first=Mark|title=Tricks of the Medieval Trades|year=2018|location=London|publisher=Archetype Publications|isbn=978-1-909492-65-3|pages=94|url=https://archive.org/details/sample-tricks-of-the-medieval-trades/page/n3/mode/2up}}</ref><ref>{{cite book|last=Riddervold|first=Astri|title=Lutefisk, Rakefisk and Herring in Norwegian Tradition|year=1990|location=Oslo|publisher=Novus Press|isbn=82-7099-164-3|pages=24–29|url=https://archive.org/details/lutefiskrakefisk0000astr/page/24}}</ref>

== Uses ==

=== Food ===
[[File:Preparing for Christmas 1950 (JOKAMT2Kot06-4).tif|thumb|A Finnish woman preparing a ''lutefisk'' or lye-cured fish]]
Lyes are used to [[Curing (food preservation)|cure]] many types of food, including olives (making them less bitter), canned [[mandarin orange]]s, [[lye roll]]s, [[century egg]]s, [[pretzel]]s, candied pumpkins, and [[bagel]]s.

Lye is the curing agent and namesake of the traditional Nordic [[lutefisk]], a type of preserved fish. They are also used as a tenderizer in the crust of baked Cantonese [[Mooncake|moon cakes]], in "[[zongzi]]" ([[glutinous rice]] dumplings wrapped in bamboo leaves), in chewy southern [[Chinese noodles]] popular in Hong Kong and southern China, and in Japanese [[ramen noodles]]. In the Philippines, lye is used in the making of [[kutsinta]], a type of rice cake, and [[pitsi-pitsî]].<ref name="philrice">{{cite web|url=http://www.pinoyrkb.com/ricerecipe/Puto-at-Kutsinta.html|title=Puto|work=Rice Recipes|publisher=Philippine Rice Research Institute|access-date=15 January 2015|archive-url=https://web.archive.org/web/20141125193706/http://www.pinoyrkb.com/ricerecipe/Puto-at-Kutsinta.html|archive-date=25 November 2014|url-status=dead}}</ref> In [[Assam]], extensive use is made of a type of lye called ''khar'' in Assamese and ''karwi'' in [[Boro language (India)|Boro]], which is obtained from the ashes of banana stems, roots, and skins. It is used in cooking, curing, as medicine, and as a substitute for soap. Lye made out of wood ashes is also used in the [[nixtamalization]] process of [[hominy]] corn by the tribes of the Eastern Woodlands in [[North America]].<ref name="Hominy Foodway of the Historic Native Eastern Woodland">{{cite web|url=https://muse.jhu.edu/article/583900/pdf|publisher=Native South|title=Rachel Briggs "Hominy Foodway of the Historic Native Eastern Woodlands"|date=2015}}</ref>

In the [[United States]], food-grade lye must meet the requirements outlined in the [[Food Chemicals Codex]],<ref>{{cite web|url=http://www.usp.org/foods/food-ingredient-reference-materials|title=Food Chemicals Codex}}</ref> as prescribed by the [[Food and Drug Administration]].<ref name=FDA>{{cite web|url=https://www.fda.gov/regulatoryinformation/lawsenforcedbyfda/federalfooddrugandcosmeticactfdcact/fdcactchapterivfood/default.htm|archive-url=https://web.archive.org/web/20170404011406/https://www.fda.gov/RegulatoryInformation/LawsEnforcedbyFDA/FederalFoodDrugandCosmeticActFDCAct/FDCActChapterIVFood/default.htm|url-status=dead|archive-date=April 4, 2017|publisher=US Food and Drug Administration|title=FD&C Act Chapter IV: Food|date=3 November 2018}}</ref> Lower grades of lye that are unsuitable for use in food preparation are commonly used as [[Drain cleaner|drain cleaners]] and oven cleaners.<ref name="FDA"/>{{Page needed|date=November 2014}}

=== Soap ===
Both sodium hydroxide and potassium hydroxide are used in making [[soap]]. Potassium hydroxide soaps are softer and more easily dissolved in water than sodium hydroxide soaps. Sodium hydroxide and potassium hydroxide are not interchangeable in either the proportions required or the properties produced in making soaps.{{citation needed|date=October 2024}}

"Hot process" soap making also uses lye as the main ingredient. Lye is added to water, cooled for a few minutes and then added to oils and butters. The mixture is then cooked over a period of time (1–2 hours), typically in a [[slow cooker]], and then placed into a mold.

=== Beauty ===
Lye, like other [[hydroxide]]-based products, is also used as a hair [[relaxer]] and straightener. Lye relaxers break a third of the chemical bonds in the hair strand and cause the hair to swell. Rinsing and then heating the hair straightens the strands.<ref>{{Cite book |last=Winter |first=Ruth |url=https://books.google.com/books?id=BamdwoBWBIMC&dq=lye+hair+relaxers&pg=PA271 |title=A Consumer's Dictionary of Cosmetic Ingredients, 7th Edition: Complete Information About the Harmful and Desirable Ingredients Found in Cosmetics and Cosmeceuticals |date=2009-10-20 |publisher=Harmony/Rodale/Convergent |isbn=978-0-307-45111-8 |language=en}}</ref> Due to their high [[pH]], they often cause scalp irritation.<ref>{{Cite book |last=Draelos |first=Zoe Diana |url=https://books.google.com/books?id=pvdWEAAAQBAJ&dq=lye+hair+relaxers&pg=PA335 |title=Cosmetic Dermatology: Products and Procedures |date=2022-03-21 |publisher=John Wiley & Sons |isbn=978-1-119-67683-6 |language=en}}</ref><ref>{{Cite book |last=Davis-Sivasothy |first=Audrey |url=https://books.google.com/books?id=WQAZAgAAQBAJ&dq=lye+hair+relaxers&pg=PA193 |title=The Science of Black Hair: A Comprehensive Guide to Textured Hair |date=2011-04-11 |publisher=SAJA Publishing Company |isbn=978-0-9845184-2-5 |language=en}}</ref> Though no-lye solutions, which use [[guanidine]] or [[lithium hydroxide]], produce less scalp irritation, they may cause brittleness due to calcium deposits.<ref>{{Cite book |last1=Aguh |first1=Crystal |url=https://books.google.com/books?id=5DGuDQAAQBAJ&dq=guanidine+hair+calcium+deposits&pg=PA17 |title=Fundamentals of Ethnic Hair: The Dermatologist's Perspective |last2=Okoye |first2=Ginette A. |date=2016-12-06 |publisher=Springer |isbn=978-3-319-45695-9 |language=en}}</ref>

People of African descent have used lye to relax or straighten hair since the nineteenth century.<ref>{{Cite book |last1=Byrd |first1=Ayana |url=https://books.google.com/books?id=jpdqmtO2IycC&q=lye |title=Hair Story: Untangling the Roots of Black Hair in America |last2=Tharps |first2=Lori |date=2002-01-12 |publisher=Macmillan |isbn=978-0-312-28322-3 |language=en}}</ref> Black men used lye-based formulations to [[conk]] their hair, and black entrepreneurs sold such formulations under names like Konkalene; [[The Autobiography of Malcolm X]] includes an account of Malcolm X receiving his first lye conk.<ref>{{Cite book |last1=Byrd |first1=Ayana |url=https://books.google.com/books?id=jpdqmtO2IycC&q=lye |title=Hair Story: Untangling the Roots of Black Hair in America |last2=Tharps |first2=Lori |date=2002-01-12 |publisher=Macmillan |isbn=978-0-312-28322-3 |language=en}}</ref> The [[Johnson Products Company]] introduced industrially produced lye-based relaxers for [[:Category:African-American hair|African American salon hair care]] in the 1950s; Ultra Wave was marketed to men and Ultra Sheen was marketed to women, and the company represented 80% of the chemical relaxer market through the 1960s. In 1971, Johnson Products became the first black-owned company on the [[American Stock Exchange]].<ref>{{Cite book |last=Draelos |first=Zoe Diana |url=https://books.google.com/books?id=pvdWEAAAQBAJ&dq=lye+hair+relaxers&pg=PA335 |title=Cosmetic Dermatology: Products and Procedures |date=2022-03-21 |publisher=John Wiley & Sons |isbn=978-1-119-67683-6 |language=en}}</ref>

=== Household ===
[[File:Lejia de ceniza.jpg|thumb|A jar of homemade wood ash lye]]
Lyes are also valued for their cleaning effects. Sodium hydroxide is commonly the major constituent in commercial and industrial [[Cleaning agent|oven cleaner]]s and clogged [[Chemical drain cleaners#Alkaline drain openers|drain opener]]s, due to its [[fat|grease]]-dissolving abilities. Lyes decompose greases via [[Ester hydrolysis|alkaline ester hydrolysis]], yielding [[water-soluble]] residues that are easily removed by rinsing.

=== Tissue digestion ===
Sodium or potassium hydroxide can be used to digest tissues of animal carcasses. Often referred to as [[Alkaline hydrolysis (death custom)|alkaline hydrolysis]], the process involves placing the animal carcass into a sealed chamber, adding a mixture of lye and water and the application of heat to accelerate the process. After several hours the chamber will contain a liquid with coffee-like appearance,<ref name="Ayres">{{citation |last=Ayres |first=Chris |title=Clean green finish that sends a loved one down the drain |url=https://www.thetimes.com/article/clean-green-finish-that-sends-a-loved-one-down-the-drain-9qdc6bjbfl8 |newspaper=[[The Times]] |date=27 February 2010 |access-date=20 February 2013}}</ref><ref name="carcassdisposal">{{citation |last1=Thacker |first1=H. Leon |last2=Kastner |first2=Justin |date=August 2004 |chapter-url=http://fss.k-state.edu/FeaturedContent/CarcassDisposal/PDF%20Files/CH%206%20-%20Alkaline%20Hydrolysis.pdf |title=Carcass Disposal: A Comprehensive Review |chapter=Chapter 6 |publisher=National Agricultural Biosecurity Center, [[Kansas State University]] |access-date=8 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20090206014343/http://fss.k-state.edu/FeaturedContent/CarcassDisposal/PDF%20Files/CH%206%20-%20Alkaline%20Hydrolysis.pdf |archive-date=6 February 2009}}</ref><ref>{{cite web|author1=Saqib Mukhtar |author2=Frederick O. Boadu|author3=Yanhong H. Jin|author4=Won-Bo Shim|author5=Tom A.Vestal|author6=Cody L. Wilson|title=Managing Contaminated Animal and Plant Materials Field Guide on Best Practices|url=http://iiad.tamu.edu/wp-content/uploads/2012/06/ConMat.pdf|publisher=Texas A&M Agrilife Extension Service|access-date=2 November 2014|pages=233–259|date=17 July 2009}}</ref> and the only solids that remain are very fragile bone hulls of mostly [[calcium phosphate]], which can be mechanically crushed to a fine powder with very little force.<ref>{{cite web|last=Wilson|first=Joseph H.|title=The History of Alkaline Hydrolysis|url=http://www.goodfuneralguide.co.uk/wordpress/wp-content/uploads/2013/09/History-of-Alkaline-Hydrolysis.pdf|publisher=Joseph H. Wilson|access-date=2 November 2014|archive-url=https://web.archive.org/web/20141102140502/http://www.goodfuneralguide.co.uk/wordpress/wp-content/uploads/2013/09/History-of-Alkaline-Hydrolysis.pdf|archive-date=2 November 2014|url-status=dead}}</ref><ref name="Roach">{{cite book |last=Roach |first=Mary |date=2004 |title=Stiff: The Curious Lives of Human Cadavers |location=New York |publisher=[[W. W. Norton & Company|W.W. Norton & Company]] |isbn=0-393-32482-6}}</ref> Sodium hydroxide is frequently used in the process of decomposing [[roadkill]] dumped in landfills by animal disposal contractors.<ref name="carcassdisposal"/> Due to its low cost and easy availability, it has also been used to dispose of corpses by criminals. [[Italy|Italian]] [[serial killer]] [[Leonarda Cianciulli]] used this chemical to turn dead bodies into soap.<ref>{{cite news |url=https://www.bbc.co.uk/news/magazine-27257822 |title=Sodium: Getting rid of dirt - and murder victims |date=3 May 2014 |publisher= [[BBC News]]}}</ref> In Mexico, a man who worked for drug cartels admitted to having disposed of more than 300 bodies with it.<ref>{{cite news | url = https://www.washingtonpost.com/wp-dyn/content/article/2009/01/26/AR2009012602190.html | first = William| last = Booth | title = 'Stewmaker' Stirs Horror in Mexico | newspaper = [[Washington Post]] | date = January 27, 2009}}</ref>

=== Fungus identification ===
{{Main|Chemical test in mushroom identification}}

A 3–10% solution of [[potassium hydroxide]] (KOH) gives a color change in some species of mushrooms:
* In ''[[Agaricus]]'', some species such as [[Agaricus xanthodermus|A. xanthodermus]] turn yellow with KOH, many have no reaction, and ''[[Agaricus subrutilescens|A. subrutilescens]]'' turns green.
* Distinctive change occurs for some species of ''[[Cortinarius]]'' and [[boletes]]

== Safety ==
{{More citations needed section|date=November 2014}}

=== First aid ===
When a person has been exposed to lye, sources recommend immediate removal of contaminated clothing/materials, gently brushing/wiping excess off of skin, and then flushing the area of exposure with running water for 15–60 minutes as well as contacting emergency services.<ref name="CCOHS">{{cite web |url=http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/sodium_hydroxide.html |title= Sodium Hydroxide | publisher = [[Canadian Centre for Occupational Health and Safety]] |date=20 May 2022 |website= CCOHS.ca}}</ref>

=== Protection ===
[[Personal protective equipment]] including safety glasses, chemical-resistant gloves, and adequate ventilation are required for the safe handling of lye. When in proximity to lye that is dissolving in an open container of water, the use of a vapor-resistant face mask is recommended. Adding lye too quickly can cause a runaway thermal reaction which can result in the mixture boiling or erupting.

=== Storage ===
Lye in its solid state is [[deliquescent]] and has a strong affinity for moisture in the air. As a result, lye will dissolve when exposed to open air, absorbing large amounts of atmospheric moisture. Accordingly, lye is stored in air-tight (and correspondingly moisture tight) containers. Glass is not a good material to be used for storage as severe alkalis are mildly corrosive to it. Similar to the case of other corrosives, the containers should be labeled to indicate the potential danger of the contents and stored away from children, pets, heat, and moisture.

=== Hazardous reactions ===
The majority of safety concerns with lye are also common with most corrosives, such as their potentially destructive effects on [[tissue (biology)|living tissue]]s; examples are the [[skin]], [[flesh]], and the [[cornea]]. Solutions containing lyes can cause [[chemical burn]]s, permanent injuries, scarring and [[blindness]], immediately upon contact. Lyes may be harmful or even fatal if swallowed; ingestion can cause [[esophageal stricture]]. Moreover, the [[solvation]] of dry [[solid]] lye is highly [[exothermic]] and the resulting [[heat]] may cause additional burns or ignite flammables.

The reaction between sodium hydroxide and some metals is also hazardous. [[Aluminium]], [[magnesium]], [[zinc]], [[tin]], [[chromium]], [[brass]] and [[bronze]] all react with lye to produce [[hydrogen]] gas. Since hydrogen is [[flammable]], mixing a large quantity of lye with aluminium could result in an explosion. Both the potassium and sodium forms are able to dissolve copper.

== References ==
{{reflist}}

== Further reading ==
* {{cite book |last=McDaniel |first=Robert |title=The Elegant Art of Handmade Soap: Making, Scenting, Coloring, and Shaping |publisher=Krause Publications |location=Iola, WI |year=1997 |isbn=0-87341-832-8}}

== External links ==
* {{cite web |url=https://www.fda.gov/opacom/laws/fdcact/fdcact4.htm |archive-url=https://web.archive.org/web/20000824071619/http://www.fda.gov/opacom/laws/fdcact/fdcact4.htm |url-status=dead |archive-date=August 24, 2000 |title=Federal Food, Drug, and Cosmetic Act |publisher=US Food and Drug Administration}}
* {{cite web |title=Food Chemicals Codex |url=http://www.usp.org/fcc/ |url-status=dead |publisher=United States Pharmacopeia |access-date=30 January 2008 |archive-url=https://web.archive.org/web/20120201141105/http://www.usp.org/fcc/ |archive-date=1 February 2012}}

{{Authority control}}

[[Category:Hydroxides]]
[[Category:Household chemicals]]
[[Category:Deliquescent materials]]
[[Category:Desiccants]]
[[Category:Soaps]]
[[Category:Sodium compounds]]

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