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  • Writer's pictureArwen Falvey

I Cannot Tell a Lye!

A little soap chemistry!

Soap is a complicated chemical process that often is misunderstood.

One of the most common questions I get about my soap is if it is made with lye. Lye, or sodium hydroxide (NaOH), has a notorious reputation for being very high on the PH scale (or a strong base) and when it comes into contact with skin it burns. Naturally the idea of putting such a thing in a skin care product seems absurd and causes a great deal of alarm for anyone who isn't acquainted with the fundamental chemistry of soap making. So here is a quick, and hopefully not completely boring, explanation of the use of lye in soap!

My soap is made with lye. But here's the important thing... ALL SOAP IS MADE WITH LYE. IF IT DIDN'T INVOLVE LYE THEN IT ISN'T SOAP!! Many of the famous manufactured "soaps" you find on the shelves of the grocery store are not soap at all in fact. If you look closely at their labels they are usually called "cleansing bars" or "facial bars" or something equally ambiguous so that you never realize that what you're using isn't soap but rather a collections of chemicals and detergents masquerading as soap. If you meet a handmade soap maker who claims they don't use lye in their soap, it is likely they are using a melt-and-pour soap base, which comes pre-made and is simply melted down, mixed with colour and fragrance and poured into a mold. Because the soap maker themselves doesn't encounter the lye does not mean there was no lye, however. Lye would have been used in producing the base to begin with because ALL SOAP IS MADE WITH LYE.

But if it has lye in it won't it burn me??

No. Not if the soap has been made correctly. If you took chemistry in high-school some of this next bit should ring a bell, and if not don't worry, it's pretty simplified and fairly easy to follow even without having taken a chemistry class.

One of the fundamentals of chemistry is: An Acid + A Base = A Salt.

So if you add something with a low PH, like chloride (which is deadly to ingest), with something that has a high PH, like sodium (which is also deadly to ingest), you end up with sodium chloride (NaCl) which is more commonly known as table salt. That's right! Two chemicals that would kill you alone are routinely combined into one of the most common flavourings in the world! The same principle works for soap as well. If you combine lye (a base) with the fatty acids in various vegetable oils (an acid) and allow a natural process known as "saponification" to occur, you wind up with soap, which is a relatively harmless salt. All of the lye will react with the oils and saponify into soap, leaving no residual lye in the resulting bar.

But how can you be sure the resulting soap doesn't contain residual lye?

There is a very long, complicated chemical calculation that goes into making a soap that I won't detail here, but suffice it to say that it is meticulously balanced to determine the precise amount of oils required to react ALL of the lye, leaving none behind. Then, just to be absolutely certain, I do something known in soap making circles as "super-fatting". That is the process of adding 5% to 10% more oil than is required. This ensures that the resulting soap will have NO RESIDUAL LYE and will rather have an excess of free oils instead. Free oils in a soap can provide all kinds of soothing, nourishing, and cleansing properties and have the added benefit of ensuring the saponification of all the lye.

What happens if your calculations are wrong?

The super-fatting is excellent for guarding against any miscalculation, but soap is a complicated process and things like time, temperature, curing, fragrance, and additives all effect the calculation in ways that may not always be foreseen. That's where PH testers come into play! The old fashioned way of checking for a lye heavy soap is to touch a bar to the tip of your tongue. That's right, and trust me when I tell you it tastes like soap. But if your tongue gets a little zap from the soap that indicates an excess of lye in the bar. Nowadays we have easy access to litmus paper and other PH testers that make the use of one's tongue unnecessary (thank goodness). Each and every batch of soap is tested for excess lye with PH paper and allowed to cure for at least 4-6 weeks before being wrapped and made available for sale.

So there you have it. All soap is made with lye but, if your soap maker is worth their salt (pun intended) there is no lye left in the soap when they are done. Next time you go to buy a soap don't be frightened away from a luxurious handmade soap just because it is made with lye, because all the best soaps are!

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