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What Is Lye?

By S. Mithra
Updated May 17, 2024
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Lye is a caustic, alkaline chemical that is useful for many purposes but also is hazardous. It can dissolve sticky substances such as fat and has a high degree of reactivity with other materials. Modern lye typically is the chemical sodium hydroxide, but potassium hydroxide was once the chemical compound that was commonly used. Whether in a flake, granular or liquid form, it is very dangerous and can cause damage to surfaces and people. Despite its hazardous nature, it is used in many common household products, such as laundry detergent and oven cleaner, and is even used to cure foods such as pretzels, green olives and mandarin oranges.

Production

Sodium hydroxide is created using a chemical reaction between soda, or sodium carbonate, and calcium hydroxide, or lime. In raw form, it is made into solid flakes, chips or grains. Chemical suppliers provide sodium hydroxide to manufacturers for use in the making of a wide variety of products, such as fabric, paper, hand soap, metal polishers and drain de-cloggers.

History

Before the modern manufacture of lye, people were able to make it out of raw materials. For thousands of years, people have used types of lye for making soap and tanning hides. They burned certain hardwoods at a very high temperature to make white ashes. Water, mixed with a bit of baking soda, then was used to penetrate the ashes and remove the lye that they contained. When the ashes were filtered out, the water would hold enough lye for purposes such as dissolving the fat left on animal furs or mixing with other ingredients to make body soap.

Dangers

This is one of many poisonous products that can be found in homes and that should be kept out of the reach of children and used only as directed. For example, a person should carefully follow the directions to clean sterling silver with a lye-based polish, because even the fumes can be dangerous. Lye-based products such as drain de-cloggers and paint stripper should never be used without proper air circulation.

Caustic lye products pose other dangers to surfaces. They can dissolve substances to the user's advantage, such as hair clogs in a shower drain, as well as to the user's detriment, such as the adjacent shower curtain. In fact, these products can damage and corrode paint, metal, cloth, plastic and especially skin. It can be so reactive that, in its solid form, it should be kept away from metals, such as aluminum, and the open air. It usually is non-combustible when dry, but it could ignite and cause a fire when mixed with water.

What Is Lye Used For?

Lye has a wide variety of different uses, ranging from everyday household applications to food curing agents to animal hide tanning. Initially, lye would be drawn out of the ashes of certain hardwoods in a long and arduous process. Only a small amount of lye would be available for tanning hides and making soap in the early days. Now, modern manufacturing produces lye in many different forms. Lye comes in flakes, powders, granules, pellets, liquids, microbeads, or solid forms. Depending on how it is produced, it can be used for a variety of applications, including:

  • Hand soap
  • Pretzel cure
  • Draining agent
  • Paint stripper
  • Silver polish
  • Lye rolls
  • Laundry detergent
  • Oven cleaner

What Does Lye Do?

Lye is a highly reactive alkali, and it is a hazardous chemical that, in large quantities, can cause significant damage. However, small and regulated amounts can be used as food curing agents. This highly reactive alkali is soluble in water and produces caustic base solutions. Practically, it is used to quickly dissolve sticky and greasy substances that are difficult to remove, such as grease or clogged drains.

Is Lye Dangerous?

Despite being used in food curing processes, lye is extremely dangerous. Lye can be included in food processing because it is carefully regulated and combined with other ingredients. It is also because the base formula for lye has changed slightly over the years. Lye began as potassium hydroxide, and now, lye is generally sodium hydroxide instead. Lye in food processing much be stringently documented and monitored.

Lye in other applications is just as dangerous. Lye is known for its quick and powerful ability to dissolve fat and grease. It can also severely affect human tissue, ruin surfaces, and paint. While it may effectively unclog the drain, it is possible that if the drain is old, it could continue to eat through the rest of the pipe, causing an entirely different issue. Before using lye in your drains, consult with a plumber.

What If Lye Gets on You?

Lye can cause severe damage to your body if you come into contact with the hazardous material. Contact emergency services immediately for help. As you wait, remove any contaminated clothing. Wipe any excess away lye from the affected area.

To prevent contact with lye, wear protective equipment and always work in a well-ventilated area. Never work with lye alone. Lye is a highly reactive alkali. The slightest bit of water in contact with lye can cause a violent reaction. A large amount of water in contact with lye can cause water to boil. Lye is also corrosive. Despite it being in a sealed container, it can still be dangerous without you knowing it. Depending on the container and the amount of time it has been stored, the container could be compromised.

Can Lye Cause Injuries?

Because lye is a highly reactive and corrosive material, if you are not careful, it can also cause serious injuries. Always work with another person and follow safety protocols carefully. Some injuries caused by contact with lye include:

  • Chemical burns
  • Scarring
  • Esophageal stricture
  • Tissue damage
  • Lung damage
  • Hypovolemic shock
  • Blindness
  • Pulmonary insufficiency

Is Soap Made of Lye?

A common misconception about lye and soap is that soap is made from lye, and the assumption is incorrect. Instead, soap is made with lye. This update is good news because people can become very bewildered to think such caustic ingredients are in their self-care routines.

Soap is made through a process called saponification. In this process, lye and triglycerides combine. During this combination, the lye corrodes the fat in the molecules and connects with other parts. The resulting chemical reaction creates both soap and glycerin. Neither of the original ingredients remains in a chemical reaction, only the results of the reaction and the byproducts. Therefore, both the lye and the triglycerides are removed from the end product you use as soap.

Many people are concerned about the use of lye in their soap-making process. This concern is primarily based on a misunderstanding. The truth is that all true soap is made with lye in the process. If it is not made with lye in the process, it is something other than soap.

Many people are unaware that chemical reactions need to happen for your skin to benefit from soap or a soap-like product. Without the reaction, your skin might not be cleansed or moisturized by that product. Moisture retention and cleansing properties are integral for maintaining the health of your skin.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

By anon987913 — On Feb 06, 2015

Will mixing lye with garden soil, and watering it, killbBroad mites and russet mites?

By anon933871 — On Feb 18, 2014

Will lye dissolve "flushable" baby wipes?

By anon313436 — On Jan 11, 2013

You should have used limes under the cabin! It is not caustic like lye, nor as dangerous. Lime can be used on your lawn to turn acidic soil to alkaline soil. Make sense? I believe it would have neutralized the odor, and the next person going under there would feel a lot safer!

By anon301199 — On Nov 02, 2012

Can lye be used to make a solid soap?

By anon283080 — On Aug 02, 2012

Will lye keep snakes away?

By anon268905 — On May 15, 2012

If a person uses lye and oil to kill groundhogs, can it kill my cats? I don't know what kind of oil is being used but she said she was using lye. One of my cats has already passed and now another is sick.

By anon264275 — On Apr 27, 2012

How does lye react to different metals? Which metals can withstand it and which cannot? What other substances will dissolve when in constant contact with it. Example: 1 tablespoon lye, 1 pint water; or 1 tablespoon lye and 1 quart water with a 12-volt charge running through it.

By anon221266 — On Oct 11, 2011

Don't sprinkle lye on human waste, or leaves. Use lime. Just regular lime (powder or a bead) like they use on farms. Much better and a little safer. Be careful if you use powder lime like for ag use. Keep it out of your nose and eyes and off your skin.

These types of applications are not really suitable for lye - while lime should work fine.

By anon209182 — On Aug 25, 2011

Lye is used every day in homemade soaps and even more so in the preparation of pretzels. Pretzels are dipped down into a lye solution of lye and water, and when baked, these pretzels have a crispier, more appealing crust to them.

By anon209180 — On Aug 25, 2011

I would like to make a quick correction to whoever was "anon177560" Lye is Lye, whether in powder form, liquid form or in micro beads, and when in contact with your skin it still burns! As a matter of fact, a liquid lye solution such as lye that has been mixed with a pint or quart or gallon of water will have a slightly weaker effect on skin since it is diluted! Lye in a powder form is in its strongest form! It is concentrated at that point.

By anon207312 — On Aug 19, 2011

My son works pouring lye in water to mix stucco, for houses. He recently broke out with bumps and he's itching a lot on both arms. What to do?

By anon198183 — On Jul 19, 2011

Can lye kill bedbugs?

By anon187689 — On Jun 18, 2011

What is the taste of lye?

By anon181179 — On May 28, 2011

I had a sewer pipe leak under my cabin. We did not know about it until a lot of raw sewage leaked out. The leak has been repaired. However, now that the weather has turned hot it smells bad. Will sprinkling lye over the raw sewage get rid of the odor?

By anon177560 — On May 18, 2011

Lye is a chemical when its mixed with water it can cause chemical burns because of the reaction it has. lye is a base and is neutralized by an acid, vinegar. When Lye is in powder form it is completely harmless until it comes in contact with water.

By anon160723 — On Mar 16, 2011

Lye is water poured over wood ash. I suppose it can be considered a chemical but it is naturally made.

By Jaedsen Laroga — On Mar 07, 2011

some say that homemade lye soap is considered one of the mildest, non-irritating soaps. Is that true?

By Jaedsen Laroga — On Mar 07, 2011

1. how is it possible to use lye water in making soap?

2. if lye has a chemical reaction in heat, why is it used to make food?

By anon157317 — On Mar 02, 2011

I have a small circle ham bone wedged in my garbage disposal. Can't get it out. Can I dissolve it with lye or some other chemical?

By anon135416 — On Dec 18, 2010

Lye is a chemical and when mixed with another chemical becomes something else. This may sound obvious but it would also answer several questions on here.

Lye in the making of soap, preparing a hide for tanning, and questions of danger to human tissue, is due to its denaturing qualities; it has the ability to disassociate the hydrophobic residues of bilaminar phospholipid bilayers, found in animal(including human) tissue.

Therefore, one is left with a hydrophilic and hydrophobic end, which is the principle behind soap as the hydrophilic end sticks to water and the hydrophobic end sticks to our skin bringing the water in closer contact.

Once lye is in a different solution it is a different solution or suspension. And therefore danger or safety would be based on the substrate. Hope this helps.

By anon128835 — On Nov 21, 2010

if lye water is not safe, why i did I see a recipe with lye water requirements?

By anon122772 — On Oct 29, 2010

anon447: You cook your food with fire but wouldn't put your hand in the fire. Same principle applies. The fire and lye produce a chemical reaction. The result is safe to consume; you just don't want to partake in the reaction yourself. (Similarly, if the food is too hot don't eat it; if there's too much unreacted lye left over, don't eat it.)

Terms like "poisonous" are gross generalizations.

If something is labeled poisonous it doesn't mean it should never be used; it just means it should never be used by somebody who doesn't understand exactly what, why, and how they're using it.

By anon87376 — On May 30, 2010

Does vinegar neutralize a burn caused by lye?

By anon74405 — On Apr 01, 2010

4 cups of water = 1 liter.

pH 12 = pOH of 2 = 10^(-2) mol/L hydroxide = 0.01 mol/L

0.01 mol of sodium hydroxide (NaOH) = 0.4 g

Therefore to make a solution of pH 12 in 1 liter of water you would need 0.4 g of NaOH.

By anon61961 — On Jan 23, 2010

If I have four cups of water, how much lye should I put in to make it a pH of 12?

By anon58185 — On Dec 30, 2009

Lye is a poison and I don't understand why the Filipinos mixed it with food like kutsintas (rice cake).

By anon39479 — On Aug 02, 2009

Have small dry well which is inaccessible, but it has backed up with leaves and other debris. Could i possibly add lye to dissolve the blockage?

By anon36766 — On Jul 14, 2009

is lye soap made w/pig lard OK to be absorbed into our bodies? what about the bad effects of pig fat, the antibiotics and hormones given to these pigs? Way back when, they fed pigs a proper diet w/out chemicals.

By anon29174 — On Mar 28, 2009

You can understand what lye is if you understand a few simple concepts about acids and bases. Lye is just the common word for NaOH, sodium hydroxide, the strongest base. This is the opposite chemical of HCl, hydrochloric acid, the strongest mineral acid. When mixed together they make simple salt water, but when concentrated as either acid or base, they are very dangerous to health. Both will attack and kill every living cell they come in contact with. However, HCl and NaOH have good uses around the house owing to this chemical energy.

HCl is useful for dissolving metals and some salts. They sell it at garden stores to use for cleaning concrete. You can also use it to remove rust from iron. (after which you should immediately wash then dry it)

NaOH is useful because it attacks oils and makes them soluble in water. The principal use for NaOH is to add it to fat in measured quantities to make soap. Soap is a wonderful chemical; intermediate between the highly reactive NaOH and the neutral H20, (water) it helps oils dissolve in water without being overly destructive to skin. After all, you don't want your skin chemically attacked when you clean it, you just want the dirt and oil to be made soluble so the water can wash them off. Try going a day without soap and see how much cleaning power water alone has.

The only reason to use NaOH directly is for very challenging cleaning jobs, where you want the total chemical energy available to dissolve fats. I'm using a little bit right now added to a deep frying tub. The caustic NaOH will attack those stubborn fats and turn them into soap, which I will be able to wash out later. However, the same chemical can turn my skin and subcutaneous fat to soap, which is where the danger is. Gloves are a must.

If you ever get any NaOH or HCl on your skin, you shouldn't waste time trying to neutralize with vinegar (for NaOH) or baking soda, (for HCl) but instead run the affected part of your body under continuous warm water for 5 minutes. Your best hope is to wash away all of the remaining chemical. If taken internally the same rule applies. Drink as much water as possible to dilute the chemical, then seek emergency medical attention.

By anon25800 — On Feb 03, 2009

What are the effects of Lye on the human body? I just recently read a Worn Path and the little boy in the story swallows it. His throat occasionally closes, are there any other effects?

By anon25120 — On Jan 23, 2009

How does one make the super cleaner "Mary Lou Lye" ??

By anon24626 — On Jan 15, 2009

Sodium Hydroxide (lye), is a common ingredient found in lots of things-like toothpaste! Just because in it's purest form it is dangerous doesn't mean it can't be used in weakened form to be helpful. In cosmetics, it's commonly used as a ph-balancing agent. Because it is so alkaline, a little bit in an acid-based solution balances out the ingredients and makes products more pleasant and stable.

It's a common misnomer among hairdressers that lye is in Johnson's Baby Shampoo which is just crap. I did some research into NaOH when they threw that old wives' tale at me. :) It's a safe and effective solvent, softener, and ph-balancing ingredient in the correct amount.

By anon24188 — On Jan 08, 2009

Cooking with Lye

I was hoping to find more information on the subject here, but I'm happy to share what I know so far!

1. Lye is poisonous

2. Lye does interesting things to texture food

In pretzels, rolls, noodles, etc. not a lot of lye is used. (A strong base, kansui, is used in making ramen. It gives the noodles its characteristic yellow color.) In Asian cooking, especially in desert making, lye water is called for and is used by the teaspoon in a lot of recipes. As for lutefish, lye seems to be used in the drying process, and to make the fish suitable for consumption, the fish must be bathed several times in clean water.

What would be more interesting to know is what pH range could be considered safe for consumption. Strong acids and bases have their hazards, but I imagine that during the cooking process the pH and chemical composition of the finished product changes drastically.

By fgagrargg — On Jan 05, 2009

Does Vinegar neutralize a burn caused by lye?

By jeffreyirvin — On Dec 17, 2008

im a scrapper and i came across hard drive that have platinum on them i was told i could use lye on then to eat away the aluminum will it work or not?

By anon18188 — On Sep 16, 2008

I came in contact with lye. i called an Ambulance. I have difficulty breathing w/ a respiration of 18.

after they gave 4 liters of Oxygen. I'm okay. did I have a panic attack? or cause by a lye chemical?

By anon15548 — On Jul 14, 2008

I have paint pants that have dried paint on them, Will lye clean them and if so how do I mix it and how long do I soak it?

By anon15494 — On Jul 13, 2008

In regard to the soapmaking... when lye is used to make soap it undergoes a chemical reaction. There is no longer lye, it is soap. This is why you should let your cold process soaps sit for up to 7 weeks though, so this chemical reaction can complete. Hope this helps you.

By anon15066 — On Jun 30, 2008

is it feasible to put lye down their holes to discourage moles?

By anon14079 — On Jun 09, 2008

Martha, I gotta ask... if you were sprinkling the lye because of the smell from the dead rodents, and you were able to actually sprinkle the lye over the whole area including the carcasses... would it not have been just about as effective to remove the carcasses?

By anon11676 — On Apr 21, 2008

My son dropped a plastic/metal hotwheel down my toilet and it is stuck, I tried snaking it. Will lye work to get it unstuck? Will it dissolve the car enough to push it through with the snake?

By anon9040 — On Feb 26, 2008

I am watching a TV show and a little kid fell in Lye. He got 1st degree burns. why is it that you can use it in household products and it doesn't burn but in this situation it did?

By anon7598 — On Jan 30, 2008

i have a report to do on lye, what do i need to know?

By anon7267 — On Jan 22, 2008

Many of the questions posted show very little knowledge of chemistry. When the lye which is poisonous reacts chemically with another substance a new substance with different properties are formed. For example -- poisonous, caustic lye (sodium hydroxide) and poisonous, caustic hydrochloric acid when mixed together form sodium chloride which is also commonly called table salt which is neither caustic nor poisonous -- in fact you SHOULD eat some daily.

By anon6944 — On Jan 13, 2008

I am new to soap making and if lye is so dangerous how come people are allowed to rub it all over their body in the form of soap?

By martha — On Nov 26, 2007

Re: Lye under the log cabin: Thanks for the warning on the lye. I'll be sure to post a warning on the hatch door, just in case someone has to go under there. (You're right- there is plumbing in the crawl space) If all goes well, no one will be down there for a long, long, long time.

By anon5470 — On Nov 26, 2007

In regard to sprinkling lye under the old cabin, I am a plumber and have had several very very unpleasant experiences with lye under a building. professional flood restoration companies cannot use lye for that purpose because of the hazards associated with inhaling lye. Someday a plumber, electrician cable guy etc.. is going to have to deal with it being there. Please inform them before they do.

By martha — On Nov 01, 2007

OK- I went ahead and sprinkled the lye on the dirt floor and rodent carcasses on the cabin crawl space. The odor is gone. For now. No humans go down there, so all seems good. Worked like a charm.

By anon4773 — On Oct 31, 2007

did they ever use lye for pickling?

By martha — On Jul 12, 2007

just ordered 2 lbs. of lye to sprinkle in the crawl space of an old log cabin where mice and rodents have gone to die- hoping to get rid of the odor. No one ever goes down there. It's a dirt floor. Do I need to be concerned about anything? The lye would be exposed to air, dirt, and rodent carcasses. Since it is under the cabin, do I need to worry about fumes, or dust coming up into the air of the cabin? Should I mix it with water before I sprinkle it? What do you think?

By anon2411 — On Jul 10, 2007

there are several different grades of lye technical grade and food grade being two of them. Technical grade is over 99% pure lye and food grade is not as strong.

By anon1568 — On Jun 06, 2007

Lye is one of the ingredients in the production of noodles. If its dangerous then why is it allowed? Can somebody please explain me why?

By anon447 — On Apr 25, 2007

So what about lye used with food, as with lutefisk, the practice of soaking whitefish in a mixture of water and lye?

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