What Is The Best Way To Do An Ingredient List For Tablet Soap?

Posted by Colin Sanders on

Here's an issue that has come up a few times lately. How do list the ingredients on tablet soap?

The reason for ingredient lists on cosmetics is to enable people who have allergies to particular chemicals to identify products that might give them a problem. This is a worthy objective, and to make sure that it is indeed effective there are rules that require companies to follow a standard format in the way they list those ingredients. This makes perfect sense, but there is a slight bug in the system. If you are adding an ingredient which reacts with another ingredient to form a third chemical altogether, how should you list that?


The regulation does not specify which way you should do it. So for example you might be adding sodium hydroxide and stearic acid to a cream with the intention that they should react to form sodium stearate. The scientific answer is fairly clear. You will actually have all three chemicals in your product. So to strictly comply with the spirit of legislation, you should list sodium hydroxide, stearic acid, and the sodium stearate produced by the reaction of the two. But to do so increases the length of your ingredient list and makes it harder for the end-user to work out what is going on. I cannot think of a single instance where a company has done this for a cream formulation. The consensus seems to be that you just list the ingredients as you added them.

This doesn't seem to give anybody any trouble. So it seems like a good pragmatic interpretation of the regulations.
But that is in creams. Probably the biggest category of goods where this issue arises is in tablet soap. Soap is made by reacting sodium hydroxide with some sort of fat or oil. The chemistry of the result of this process is it pretty well known, but could give rise to a very complicated ingredient list if you let it. Imagine for example you're making a soap from olive oil. Olive oil is made up of many different components. All of these can react with sodium hydroxide to give different chemical species.

How should you produce an ingredient list for such product?

There are in fact three options, all of which I have seen used at some time or another.

1. You can simply list the written ingredients i.e. the olive oil and the sodium hydroxide.

2. You could look at the chemistry of olive oil and calculate the various quantities of all the different potential materials the reaction with sodium hydroxide could produce.

3. But the most common approach is to use a name that indicates its origin, in this case sodium olivate, but which reveals little detail. There are a whole set of these names given on the official list, and I suspect they are used for no other purpose than for labelling soap.

My personal preference would be for the first approach. I think it is a big ask to expect somebody who has a reaction to olive oil to appreciate that a soap made from olive oil gets to have it listed in a different way to a cream containing olive oil. It is also consistent with the way other parts of the industry do that ingredient lists. I think there is a lot to be said for being as straightforward as you can be with your description of your product.

I haven't done a formal survey, but my guess is that well over 90% of soap is labelled using the third approach. So I would appear to be in a minority.

I think the explanation is pretty simple. I am old enough to remember when ingredient lists first came in. When deciding how to interpret the regulations we simply looked at what other people were doing, and did that. The soap makers did the same, but came to a different consensus with the result that most of them do it the same way and different to every other category. And who can blame them. Nobody ever got fired for doing what everyone else is doing. This is one of those issues where following the crowd is probably the best strategy.

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  • But then again, it begs the question, is there any sodium hydroxide in the finished product?
    Love the blog Colin!

    Alex on
  • Well if that is your interpretation by all means go for it Francis. Out of curiosity, if you were making a soap with olive oil and sodium hydroxide, but decided to switch to buying in sodium olivate would you change your ingredient list? The chemistry of the final product would be identical.

    Colin Sanders on
  • I think that the regulation’s clear on this: “The list of ingredients shall be established in descending order of weight of the ingredients at the time they are added to the cosmetic product.”
    If you pour olive oil and sodium hydroxide into your mixer then you list them as such. If you buy sodium olivate and pour it in, then that’s what you label.

    Francis on

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