What's in Your Soap

Written by Richard M. Hamner, Ph.D. and used by permission.

Have you ever wondered just what is in that bar of soap you use? (Actually, it is just as important to ask what should be in it that isn't.) Many people don't know how soap is made or what makes one brand better than another. It is just not something that we take the time to look into. But as with most things, when you understand something, you can make smarter choices about what is best for your own use.

If you grew up on a farm, you probably watched someone make soap. They most likely used rendered lard and lye, and mixed the two in a big iron wash pot out in the yard. Farm soap took on the term "lye soap", and it got a really bad reputation for being harsh. "It didn't stop at the dirt" was the old saying.

Well, believe it or not, soap is still made by the same chemical reaction. The difference is that present-day oils and lye are more pure than what they had on the farms back when. Also, our understanding of soap chemistry is more highly developed now, and our ability to weigh and measure things precisely is much better. In short, modern soap is just a highly refined version of old fashioned soap.

Well, mostly.

There are some differences, and as you might expect, it has to do with sales and marketing. So let us set off on a short journey to understand soap. This new knowledge might make a difference in your life.

How is soap made? What are the raw materials?

Soap is made through a centuries-old chemical reaction called saponification.

Oils are reacted with a strong alkali ("lye" became the nickname for the alkali, or caustic), and the result of the reaction is soap and glycerine. Early soap makers used caustic potash, or potassium hydroxide, for the alkali because it could be made from the ashes of hardwood fires. That tended to make a soft soap, and it was used for laundry mostly. Now we use caustic soda, or sodium hydroxide, for bar soap because it allows the bar to harden more.

To let you know just how old the art of soap making really is, there is evidence that a soap-like substance was made in ancient Babylon, according to the inscriptions found on some of the clay pots excavated there. The estimated dates are about 2800 BC, making them about 48 centuries old! The inscriptions on the urns indicate that ashes were mixed with animal fats, so what they had was soap, even if it was a little crude. It is thought that the resulting substance was used on their hair rather than being used for cleaning.

A legend that comes from the days of the Roman Empire also helps to illustrate how soap is made. The story goes that the people who washed their clothes in the rivers and streams of old Italy found that their clothes got cleaner if they would go just down from the places used for burnt offerings. This makes sense, because in a burnt offering, you have all the ingredients for soap. The fire makes ashes, which contains potash, and when the rains came, caustic potash would be produced. The fat from the animal offered in the sacrifice would drip down into the ashes. Mix the two together, and you get soap. The soap would run down into the stream, and it would help to get the dirt out of your toga. A stretch of the imagination perhaps, but then most legends are.

In any case, soap making is a very old art. Here is how you do it: You mix vegetable oils or animal fats together with a water solution of a strong alkali, such as caustic soda. That's it. Then you let Mother Nature take over. The chemical reaction that ensues does the rest.

Soap Chemistry

Unless you want to formulate your own soap recipe, all you need is a very basic understanding of chemistry to understand the saponification reaction.

The oils are triglycerides. A triglyceride is made up of a glyceride ion attached to three fatty acid chains. When the caustic is mixed with the triglycerides, the fatty acids break loose from the glyceride ion and join with the sodium part of the sodium hydroxide. That forms soap. The glyceride ion joins with the hydroxide part of the sodium hydroxide, turning it into glycerine, which goes free.

So here is a short version of soap making:

[ Oils + Caustic ] yields [ Soap + Glycerine ]

The rest of the details, such as how much oil can react with how much caustic, and how you process the soap as the reaction proceeds, will all be left to those who want to do a little research. There are many good books on the subject.

Grocery Store Soap

Nearly all of the soaps that I call "grocery store" soaps start with 80% tallow and 20% coconut oil. (Tallow is rendered beef fat, whereas lard is rendered pork fat.) The oils are reacted with caustic soda, the glycerine is immediately removed while the soap is still hot, and the resulting soap is cooled and dried. Then they start adding the additives.

The 80/20 tallow and coconut oil ratio makes a soap that has come to be called "80/20 soap base", and virtually all of the major soap makers throughout the world use this as a base for their bar soap. So the only real differences among all the various bars of soap are different fragrances, colorants, and other additives.

The table below gives a list of the components in typical bar soap formulations. (There is a lot of stuff in your soap besides soap, as you can see.) Not every brand will have all of these, and some will have more.

Table 1. Typical Toilet Soap Formula Components

% Range
Surfactant Soap
Synthetic Detergent
0.0 - 20.0
Antioxidant (Preservative) BHT (Butylated Hydroxytoluene)
0.1 - 0.4
Sequesterant EDTA, DTPA
0.1 - 0.5
Whitening Agent Titanium Dioxide
0.1 - 0.5
Special Additives

Deoderant / Antibacterials

Triclosan, Triclocarban
0.2 - 1.5

Skin-feel Additives

Fatty Acids, Polyacryloates
0.5 - 10.0
Lather Stabilizers
1.0 - 5.0
Glycerine, Lanolin
0.5 - 5.0
Bar Hardening Agents NaCl, Na2SO4
0.5 - 1.5
Color Additives Various Colorants
0.01 - 0.0001
0.5 - 2.0
Fillers Starch
0 - 10.0
8.0 - 15.0

Reference: Soap Technology for the 1990's; edited by Luis Spitz, published by the American Oil Chemists Society, Champaign, Illinois, copyright 1990.

Notice a couple of things about the contents of the table. Under "surfactant" (which stands for "surface active agent", a general name for soaps and detergents), there are two types: soap and synthetic detergent. Some "soap" bars these days have detergents in them such as sodium cocoyl isethionate. More about detergents later in this article.

Next, notice that there are lots of things that have nothing to do with either getting you clean or taking care of your skin. In fact, everything in the table except the soap and the moisturizer falls in this category. These are things that are dictated by the marketing department to make the bar look a certain way or feel a certain way or smell a certain way. They help sell the soap, but they don't necessarily get you any cleaner.

What about the glycerine?

As you remember from the chemistry equation above, soap making naturally generates glycerine. Glycerine is called a humectant, meaning that it retains moisture, which makes it a natural skin moisturizer. Curiously, most of the bars of soap you see on the shelves at the grocery store don't mention glycerine as one of the ingredients. The reason is that it has been removed.

Nearly all mass-produced soap has had the glycerine removed from it. Why?
Because it can be sold as a separate commodity with perhaps a greater fiscal return than would be derived by leaving it in the soap. Glycerine is used in pharmaceuticals, cosmetics, food products, cellophane, and it is used in explosives. Remember nitroglycerine?

An interesting note about glycerine's being used in the production of explosives comes from Britain during World War II. At that time, British soap makers were regulated by their government. This was not to ensure a clean populace, but rather to ensure that the maximum amount of glycerine would be available to produce ordnance for the war effort. Soap is dynamite!

Also, as a matter of clarification, the term "glycerine soap" has become synonymous with "transparent soap", but glycerine cannot create transparency in a soap bar by itself. "Glycerine soap" is just another improperly used household word that arose from a misunderstanding. Soap is made transparent by the addition of certain alcohols and sugars. These are dissolved with pure soap and resolidified, causing the molecular structure to change, and letting the light through. Pure soap, even with lots of glycerine in it, is still opaque.

Another thing about transparent "soap" bars: some transparent bars are not even soap. Triethanolamine is an example of a surfactant that is also transparent, and it is used in some cleansing bars.

Synthetic Detergent ("SynDet") Bars

Next time you are in the grocery store, pick up a product that avoids the word "soap", but rather advertises itself as a "beauty bar" or "deodorant bar" or "body wash", and look at the ingredient list. It will say something like "sodium cocoyl isethionate" or something similar. What you will have in your hand is a bar of synthetic detergent, not soap. So, just how does this new substance compare to soap? Before we get too far into this, let's have a look at history once again.

Along about the time of The Great War (now called World War I), things got a little tense in Europe. The normal raw materials used for soap became scarce because there were blockades to shipping and imports, so they set out to create an alternative to soap. Coal was abundant, and coal can yield a type of oil that has benzene in it, similar to petroleum, and the chemists came up with a new substance. It was called linear alkyl benzene sulfonate, or LAS for short, and that was the first detergent.

LAS acts like soap because it can form an emulsion, meaning that it can mix with both oil and water. But there is a twist. Detergents don't form a bathtub ring! True soap will interact with the calcium and magnesium in hard water to form a substance called "soap curd" which is insoluble in water. It sticks to the sides of the bathtub and is hard to wash off. Detergents don't form any such substance.

Another common detergent used in body care is sodium lauryl sulfate, or SLS. SLS is used in many shampoos and body washes and bath gels. There are many other detergents that have been developed. Some are used for textiles, some for pots and pans and dishes, and some for personal care.

Who can benefit from really pure bath soap?

When would you look specifically for a soap with no additives, and one that retains all its naturally-produced glycerine? There are several instances when this would be important.

First of all, many people have allergies or sensitivities to fragrances or some of the other additives that are used in many of the bar soaps on the market. If you can determine that your skin reacts badly to those things, or if you sneeze when you use a particular soap, chances are you would benefit from using an unscented soap.

If you work outdoors a lot, or if your skin tends to be dry or sensitive, a soap with a high glycerine content could help. Hunters need soaps without any fragrances in them that might alert the game, and they also need soaps that help keep their skin from getting dry when they are out in the dry winds of winter.

Diabetics or people undergoing chemotherapy tend to have sensitive skin, and they can use soaps without additives with good result. And, if you are a person who simply wants to use pure products on your skin, you might look into some of the pure handmade soaps.


I have found a really good definition for dirt. Dirt is material that is in the wrong place (1). Tomato catsup is perfectly fine if it is on your fries, but if it gets on your shirt, it suddenly becomes dirt, and you try to remove it. Soap is the stuff that helps to get dirt out of the wrong places and back to where it should be.

(1) Jones, Mark M., et al.; Chemistry, Man and Society. W. B. Saunders Co., Philadelphia, 1972.