Sodium Hydroxide (Lye)
The Chemistry Behind Real Soap
What Is Sodium Hydroxide?
Sodium hydroxide (NaOH), commonly called lye, is a simple alkaline compound that is essential for making real soap. While the word “lye” can sound intimidating, it plays a very specific and necessary role in traditional soapmaking — and it does not remain in properly made soap.
A Brief Look at Lye’s History
Before modern chemistry, lye was made by soaking hardwood ashes in water. This produced a crude alkaline solution often called potash (from “pot ash”). Because there was no way to measure strength or purity, early soapmaking could be unpredictable — sometimes harsh, sometimes ineffective.
Modern sodium hydroxide is far more precise and consistent. It is produced from a simple saltwater (brine) solution using a controlled process called electrolysis.
How Sodium Hydroxide Is Made
Modern sodium hydroxide is made by breaking down a saltwater solution called brine.
Saltwater contains sodium chloride (NaCl) and water (H₂O). During electrolysis, an electric current separates these components into their basic parts. The sodium ions (Na⁺) combine with hydroxide ions (OH⁻) to form sodium hydroxide (NaOH).
The result is a pure, reliable alkaline compound — one that allows soapmakers to carefully control formulations and produce gentle, well-balanced soap.
Why We Use Sodium Hydroxide
When making our cold-processed soaps and shampoo bars, sodium hydroxide is dissolved in water or another water-based liquid and then mixed with natural plant oils and butters. This mixture triggers saponification, a natural chemical reaction in which:
- Oils and lye chemically transform into soap
- Glycerin is naturally created as a byproduct
Once saponification is complete, the sodium hydroxide and oils no longer exist in their original forms. They have been completely changed into a new substance called soap
Properly made natural soap contains NO free lye. All of the sodium hydroxide is used up during the reaction.
No lye--no soap. This is an important distinction: All true soap — whether handmade or commercial — is made with lye.
If a cleansing bar is made without sodium hydroxide, it is not soap. It is a synthetic detergent, often referred to as a syndet bar. Detergents cleanse in a very different way and rely on synthetic surfactants rather than the natural chemistry of soap.
The Role of Craft and Experience
The safety and gentleness of a natural soap or shampoo bar depend on:
- Accurate formulation
- Proper lye-to-oil ratios
- Adequate curing time
This is where experience matters. When soap is thoughtfully formulated and fully cured, it is mild, skin-friendly, and rich in naturally occurring glycerin.
👉 To learn more about the Chemistry of Soapmaking or How We Make Natural Soap, read our blogs:
