If you’ve spent much time reading about handmade soap, you may have come across the word glycerine. It’s often mentioned as one of the lovely things about traditionally made soap, and you’ll also find it listed as an ingredient in all sorts of skincare products.
But what actually is it? Why is it in soap? And does it really make a difference to how your skin feels?
First of all, what is glycerine?
Glycerine, sometimes called glycerol or glycerin, is a clear, colourless, slightly thick liquid that has an interesting ability to attract and hold onto water. In skincare, this makes it what’s known as a humectant.
A humectant is an ingredient that attracts and binds water, helping to keep moisture where it’s needed. Glycerine is widely used in moisturisers, lotions, creams and other cosmetic products for precisely this reason. And before you ask, yes, glycerine is a chemical. Just like water, olive oil and absolutely everything else in your bathroom.
We’ve been through this. 😂
Where does the glycerine in handmade soap come from?
Here’s the really interesting bit. I don’t need to add glycerine to my soap. It’s created naturally during the soapmaking process. When I make a batch of cold process soap, I combine oils and butters with a carefully calculated solution of sodium hydroxide.
This triggers a chemical reaction called saponification. The oils and butters contain fatty acids joined to glycerol. During saponification, those connections are broken, allowing the fatty acids to form soap while the glycerine is released.
In simple terms:
Oils and butters + sodium hydroxide = soap + glycerine
So glycerine isn’t something that has been sprinkled into the recipe afterwards to make it sound more luxurious. It’s one of the substances produced as a natural part of making soap. Clever, eh?
What happens to the glycerine?
In the traditional cold process method I use at The Soap Mine, the glycerine stays in the soap. Once the soap has been poured into its mould, cut into bars and left to cure, the glycerine remains part of the finished product. It’s simply a natural component of the bar and not an additional ingredient I need to buy or add separately. And because glycerine attracts water, it can contribute to how the finished soap holds moisture and feels during use.
It’s one of several things that influence the character of a handmade bar, alongside the oils and butters used, the amount of superfat and the overall formulation
Doesn’t all soap contain glycerine, then?
Glycerine is produced whenever traditional soap is made from oils or fats through saponification. But whether it remains in the finished product depends on how that soap is manufactured. In large-scale soapmaking processes, the glycerine is often separated out from the soap during production.
It can then be purified and used in other products, including cosmetics, toiletries and food manufacturing.
And here’s a rather unexpected fact. Glycerine recovered during large-scale soapmaking has historically been used to manufacture nitroglycerine, an explosive used in dynamite! During wartime, glycerine was such an important raw material that even ordinary fats and oils became valuable resources for the explosives industry.
So there you go. One of the by-products of making something as innocent as soap can also be used to make explosives.
Chemistry really is full of surprises. 😂
Does glycerine moisturise your skin?
This is where we need to make an important distinction. Glycerine is a well-established humectant, and in a moisturising cream or lotion, it can help support skin hydration.
But soap is a rinse-off product. You use it to wash away dirt and oils, then rinse it off with water. That means we can’t automatically assume that because glycerine has moisturising properties in a leave-on product, a bar of soap containing glycerine will have the same effect.
The overall formulation matters enormously, but glycerine doesn’t magically cancel out the cleansing effects of soap, nor does its presence automatically make a soap moisturising. Any claims that a soap actively moisturises the skin should be backed up by appropriate evidence.
Is glycerine soap different from ordinary handmade soap?
You might have seen clear or translucent bars advertised as glycerine soap. These are often made using specially formulated melt-and-pour bases containing additional glycerine and other ingredients that help create their transparent appearance. But the name can be slightly misleading, because glycerine isn’t exclusive to clear soap. Traditional cold process soap contains naturally produced glycerine too, even though the bars are generally opaque.
So a soap doesn’t have to be transparent, or specifically advertised as glycerine soap, to contain glycerine. My colourful, swirly bars might look completely different from those clear soaps, but glycerine is part of their chemistry all the same.
Another reason I love cold process soapmaking
One of the things I find fascinating about making soap is how much is happening behind the scenes. You start with oils, butters, water and sodium hydroxide, and through a chemical reaction, you create something with entirely different properties. The oils and butters become soap, glycerine is produced, and over the following weeks the bars gradually become firmer as they cure. And all of this happens before anybody gets to unwrap a bar and enjoy using it.
So the next time you pick up a bar of The Soap Mine soap, remember that there’s more going on inside it than lovely fragrance and pretty swirls.
There’s a little bit of chemistry in every bar.
Vicki x
