What is Lye?

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  • Originally Written By: S. Mithra
  • Revised By: A. Joseph
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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.


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.



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.


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.


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Discuss this Article

Post 62

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

Post 61

Will lye dissolve "flushable" baby wipes?

Post 60

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!

Post 59

Can lye be used to make a solid soap?

Post 58

Will lye keep snakes away?

Post 56

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.

Post 54

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.

Post 52

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.

Post 51

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.

Post 50

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.

Post 49

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?

Post 48

Can lye kill bedbugs?

Post 47

What is the taste of lye?

Post 45

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?

Post 44

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.

Post 43

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

Jaedsen Laroga
Post 42

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

Jaedsen Laroga
Post 41

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?

Post 40

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?

Post 39

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.

Post 38

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

Post 37

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.

Post 33

Does vinegar neutralize a burn caused by lye?

Post 32

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.

Post 31

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

Post 30

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

Post 28

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?

Post 27

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.

Post 26

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.

Post 25

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?

Post 24

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

Post 23

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.

Post 22

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.

Post 21

Does Vinegar neutralize a burn caused by lye?

Post 20

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?

Post 19

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?

Post 18

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?

Post 17

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.

Post 16

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

Post 15

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?

Post 14

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?

Post 13

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?

Post 12

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

Post 11

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.

Post 10

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?

Post 8

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.

Post 7

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.

Post 6

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.

Post 5

did they ever use lye for pickling?

Post 4

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?

Post 3

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.

Post 2

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?

Post 1

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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