What Is Lye Used For? Powder, Chemical Formula, Soap Making (2024)

• Introduction
  • What is lye?
• History
  • Where does lye come from?
• Recipe
  • How is lye made?
• Lye Uses
  • What is lye used for?
• Soap Making
  • How is lye added to soaps?
• Benefits
  • Why do we use lye in our soaps?
• Risks
  • Is lye harmful to humans?

What is lye?

Lye is a strong alkaline product used to make soaps and cleaning products and in the chemical industry. It comes in two forms, caustic soda and caustic potash. Caustic soda is sodium hydroxide with the chemical formula NaOH and caustic potash is potassium hydroxide with the chemical formula KOH.

Lye is commercially available in many forms such as lye powder, flakes, pellets, or liquid. Flakes are most commonly used to make handmade soaps. Typically, sodium hydroxide is used to make soap bars and potassium hydroxide is used to make liquid soap because potassium hydroxide does not crystallize like sodium hydroxide does.

Where does lye come from?

Lye is a natural substance present in ashes when hardwood or certain plants or seaweeds are burnt. It is extracted from the ashes by various processes that have evolved over the last few centuries.

How long has lye been used?

The use of lye for soap making and tanning hides has been in practice for at least 4800 years, from the time ancient Egyptians, Romans, and Babylonians discovered its cleansing and softening properties. Archeologists have found lye soap dating back to 2800 BCE in Babylon.

How is lye made?

Traditionally, people made lye by burning hardwood at high temperatures to produce white ashes. They then added water to the ashes and boiled it which yielded a potassium hydroxide solution. After filtering the ashes, they mixed this solution with animal tallow to make soap.

Sodium hydroxide was historically made from the ashes of sodium-rich plants such as seaweeds or glasswort plants. These ashes yielded sodium carbonate which was treated with slaked lime (calcium hydroxide) to produce sodium hydroxide.

However, these methods yielded inconsistent lye. Currently, potassium hydroxide is made by electrolysis of potassium chloride solution, and sodium hydroxide is made using normal salt (sodium chloride [NaCl]) in an equivalent process known as chloralkali.

The electrolysis/chlorarkali process involves the following steps:

1. Sodium chloride or potassium chloride is dissolved in water.
2. Graphite rods are immersed in the resulting solution.
3. The rods are connected to wires and current is passed through the rods.
4. The sodium and potassium molecules in the respective chloride solutions split from chlorine and react with hydrogen in the water forming sodium/potassium hydroxide.
5. Sodium/potassium hydroxide crystals get charged and attached to the rods. The liquid is filtered out and any remaining moisture is allowed to evaporate until only the lye crystals remain.

What is lye used for?

Lye is used for purposes as varied as baking, soap-making, and cleaning, to dissolving animal tissue. Primary lye uses include:

• Soap making: The most common use of lye is for making soap and cleaning agents. Technically, a soap without lye is not a soap as defined by the Food and Drug Administration (FDA).
• Food industry: Lye is used to cure many types of food such as meat, fish, fruits, and vegetables. Curing is the process of preserving and enhancing the flavors of food. Uses in food processing include tenderizing meats and fish, curing olives before brining, dipping pretzel and bagel dough before baking to make them crisp, softening corn for making hominy, and in the preparation of many Asian foods such as canned oranges, moon cakes, rice cakes, and noodles.
• Making of household and commercial cleaners: Lye is a major constituent of household and commercial cleaning agents used to clean ovens and unclog drains because of its cleaning effects and ability to dissolve grease.
• Industrial use: Industrial uses include the manufacture of chemicals, cleaning compounds, rayon, paper, explosives, dyestuffs, and fertilizers, for electroplating, oxide coating, metal cleaning, and petroleum refining, and as an electrolyte in alkaline batteries.
• Tissue digestion: NaOH or KOH solution can be used to dissolve and decompose dead animals such as roadkill dumped in landfills, because of its ability to break down proteins. Immersing the dead animals in the lye solution and applying heat to accelerate the process leaves only a liquid and a few fragile bones that can be easily and safely disposed of.
• Fungus identification: Lye causes color changes in some species of fungi and mushrooms. A solution of 3-10% KOH is used to identify the presence of fungus in samples of body tissue or body secretions/fluids. This is also called KOH staining.

How is lye added to soaps?

Lye is added to water, cooled down for a few minutes, and then added to oil and butter. This is cooked for 1-2 hours and then placed into a mold to make soap bars of various shapes. Colors and essential oils for fragrance may be added before pouring the soap solution into molds.

Lye chemically reacts with the fats to form soap in a process called saponification in which the fats are broken down into fatty acid chains and in the process the lye itself is neutralized. Saponification can be a cold or hot process; however, the application of heat speeds up the process.

Why do we use lye in our soaps?

Although lye is a corrosive alkali, we use it in our soaps because there is no soap without it. Lye is the base medium that is required for the chemical reaction to convert fats in tallow, oil, or butter into soap. Without lye, the oils and fats will remain just oils and fats, which cannot lather or function like soaps. Synthetic detergents may also be used to make soaps and shampoos, but these are not natural products, nor do they fall under the definition of soap.

Many cleansers that claim to be lye-free very often contain ingredients that have been processed with lye. Some of the common ingredients in soaps are sodium tallowate, sodium cocoate, and sodium kernelate, all of which have undergone processing with lye. In fact, glycerin soaps which are known to be moisturizing, just undergo another step in the process after saponification.

Health News

• Looking for Good Info on Vasectomy? Skip 'the Snip' on TikTok
• Surgery Helps Young Kids With Cerebral Palsy Walk, Regardless of Age
• New Hope for People With Aggressive Form of Lymphoma
• Robust Gut Microbiome Can Help You Fight Infections
• Microplastics Found in Human Penises
• More Health News »

Is soap made with lye safe to use on the skin?

If lye is corrosive enough to dissolve animal tissue, it naturally gives rise to questions such as:

• “Are lye soaps safe to use on skin?”
• “What does lye do to the skin?”
• “Is lye soap good for your skin?”

Lye soaps are perfectly safe to use on the skin simply because there is no lye in soap, provided the correct soap-making process has been followed.

During the process of saponification, lye and fats combine to become soap and no lye in its original form remains in properly processed and cured soap. However, the use of too much lye or improper formulation or curing process may result in soap with lye residues that can irritate and dry out the skin.

Is lye harmful to humans?

Used appropriately, lye is not harmful, either when used in soaps or when used in baking and cooking certain foods. During cooking or baking, lye reacts with carbon dioxide from the heat and forms a carbonate which is no longer present in the food product in its original form. However, a highly diluted food-grade product that meets the specifications of the Food and Drug Administration (FDA) should be used for food processing.

Although lye is a versatile substance with several applications, it is still a highly corrosive strong base with a pH of around 13 or 14 and can be harmful to humans. Exposure to the skin can cause chemical burns and serious injury to the eye. Inhalation of fumes can burn the nasal passage and airway, and accidental ingestion can cause severe injury to the throat and the digestive system that can turn fatal.

Lye should be handled with caution. Lye containers should be opened in a well-ventilated room while using protective gear because they react with the moisture in the air and release heat and caustic fumes. Lye should be stored safely in air-tight containers because it dissolves in atmospheric moisture. Adding lye too quickly to water can cause the water to boil or erupt. It also reacts with many metals and releases hydrogen which is inflammable.

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/lye

https://www.chemicalsafetyfacts.org/sodium-hydroxide/

https://pubchem.ncbi.nlm.nih.gov/compound/Potassium-Hydroxide

https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-Hydroxide

https://en.wikipedia.org/wiki/Lye