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Why Lye?

Updated: Jul 3, 2023

All ‘true’ soaps have lye, or sodium hydroxide, in them. All of them. Most soaps that you see in the grocery are actually synthetic detergent bars or syndets. If they don’t have lye (aka sodium hydroxide or potassium hydroxide) listed in the ingredients, they’re most likely syndets bars. Another tell-tale sign is the addition of glycerin! If they’ve had to add glycerin, then it’s not soap! (see the blog post called “Glycerin Rivers”.

When you start looking for lye, it’s always amusing to me how many food products actually use this caustic substance to (mostly) process them.

a grouping of several different bucket stacks, one stack with BIOHAZARD printed on the buckets

Olives, pretzels, and bagels are fairly well known to many as using lye in the processing, but did you know that canned mandarin oranges and hominy also both use lye? Wow!

Of course, lye is used in drain cleaners (I have the cleanest water pipes in town!) and oven cleaners. When you pour that drain cleaner down your drain, it combines with the grease to soften it and make it so it runs down – in other words, it makes soap in your pipes which you then just remove with water!

All of this might convince you that lye is actually a ‘safe’ product. It is anything but that, being very caustic to the skin and if it gets in contact with a human, it WILL burn you! One has to ‘suit up’ and still be very cautious when using lye. My personal ‘biohazard’ suit consists of a face shield, nitrile gloves over a long sleeve shirt, and foot coverings (usually my slippers, which is NOT recommeded!).

a chemist wearing nitrile gloves holding a plate with 6 pink globs on it

So, why lye in soap? In order for the soap to saponify it needs the caustic alkali substance to turn all of those yummy oils like coconut oil into soap! Without it, you have a bunch of oils and water and whatever stuff floating around and it’s just yucky!

Lye sparks the saponification process into action changing all of those vegetable oils or animal fats into lovely lathery soap for us to wash our hands and other parts with!

So, no reason to lie about lye! It’s used for so many things, and without it, we just wouldn’t have soap!

person with soapy hands



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