Why Lye?

Posted by Cristi Gee on

“Do you have any soaps made without lye?”

Well, no, actually.


I get this question quite often when people start looking over the products and the ingredients list. The short and simple answer is this: No lye, no soap. I hope you like science as much as I do, because we’re going to get really, REALLY technical in this post. Don’t worry, I wasn’t one of those crazy kids in school who actually liked chemistry. I adored science, but chemistry was a step too far for me. Who would’ve thought that all these years later I’d be a “mad scientist”, as my friends and family call me.


Simply put, bar soap is a sodium salt of a fatty acid. Ok, that may not have been as simple as it sounded in my head, but there will be graphics...I promise. Fat + Water + Lye = Soap (disclaimer, it’s both simple and complicated.) This is the oversimplified recipe for making soap. We all know that oil and water don’t readily mix or stay mixed. The addition of lye to the equation starts a chemical process known as saponification which turns the whole mixture into soap.

 Image Credit Brad Anderson (left image)


Fat (a.k.a. Ester, Oil - either plant or animal origin) is an acid, acidic pH

Water (a.k.a. H2O, Aqua), neutral pH

Lye (a.k.a. NaOH, Sodium Hydroxide, Caustic Soda) is a base, extremely alkaline pH


But I don’t see lye listed in the ingredients of the soap in the stores… Well, that’s a tricky one. Some companies list the sodium salt version of the ingredients that went into the pot for that particular soap recipe. For example:

Olive Oil + Water + Lye = Sodium Olivate
Coconut Oil + Water + Lye = Sodium Cocoate

It goes on and on, depending on which oils are used. Unless the product has been scientifically tested for precise levels of sodium salts, there’s no way to know what percentage of which oil has been saponified (turned into soap.) This is why we list every ingredient that goes into the pot.


The good thing is that when a soap recipe is properly formulated and is balanced, all the lye is consumed during the saponification process. No lye remains in the finished bar, but we go by FDA guidelines on this side and list everything that goes into the recipe.


Even with melt & pour soap kits that you buy from the craft store, the soap base is already saponified, so you don’t need to add any additional lye. But it was made with lye. If you meet someone who says they made soap without lye, it’s a lye (pun intended.)


So, there you have it...the oversimplified, complicated explanation of why lye is absolutely imperative in soap making.   Make today a great one. See you on the other side. ;)

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