Turn over almost any bar of soap and the ingredient list looks like a chemistry quiz. Sodium cocoate. Sodium palmate. Tetrasodium EDTA. Behind the long names, though, real soap is one of the simplest things in your house. It's made from three basic ingredients, and people have been mixing them for thousands of years.
Here's what soap is made of, what each ingredient does, what else ends up in the bar, and how to tell what's in the one in your shower.
The short answer
Soap is made of fats or oils, lye and water. When the fat and the lye meet, a chemical reaction called saponification turns them into soap and glycerin. Everything else you see on a label, like fragrance, color or skin-feel additives, is optional. Chemically, soap is a salt of fatty acids, which is why the ingredients on a soap label so often end in "-ate."
The three ingredients every soap needs
1. Fats and oils
Fats and oils are the heart of the bar, and they decide most of what you'll notice about it. Almost any fat can become soap. Soapmakers mostly use a handful of plant oils and butters, and sometimes animal fats.
- Plant oils. Olive, coconut, palm, sunflower, castor, avocado, sweet almond and rice bran oil are all common.
- Butters. Shea butter, cocoa butter and mango butter make a harder, creamier bar.
- Animal fats. Beef tallow and lard were the original soap fats, and some brands still use them. Ivory, for one, has long been made with tallow. We compared it in Dial vs. Ivory, and wrote about tallow soap too.
Every fat brings something different, so most soapmakers blend several. Here's roughly what the common ones contribute.
| Oil or fat | What it brings to a bar |
|---|---|
| Olive oil | Gentle, creamy lather and a mild feel. A bar made only from olive oil is castile soap. |
| Coconut oil | Big, fluffy bubbles and strong cleansing. Too much can feel stripping. |
| Palm oil | A hard, long-lasting bar with steady, creamy lather. |
| Castor oil | Boosts and stabilizes lather. Used in small amounts. |
| Shea and cocoa butter | Hardness and a rich, conditioning feel. |
| Sunflower oil | A soft, conditioning feel. Works best blended with harder oils. |
| Tallow and lard | A hard, white bar with creamy, stable lather. |
2. Lye
Lye is the ingredient that makes soap possible. It's a strong alkali, and there are two kinds. Sodium hydroxide makes hard bar soap. Potassium hydroxide makes soft and liquid soap. You can't make true soap without one of them, a point we cover in can you make soap without lye.
That sounds alarming, since lye is caustic enough to burn skin. The key is that it gets used up. When a soapmaker measures carefully, all of the lye reacts with the oils, and none is left in the finished, cured bar. For the full story of lye itself, read what is lye soap made of.
3. Water
Water dissolves the lye so it can mix evenly into the oils. Most of it evaporates while the bars cure, which is why handmade soap rests for several weeks before it's ready. Some soapmakers swap part or all of the water for another liquid, like goat milk, beer, coffee or tea, for a different color, feel or story. See goat milk soap and beer soap for two favorites.
What happens when they're mixed
Fats are made of molecules called triglycerides, three fatty acids attached to a glycerol backbone. Lye breaks those bonds apart. The fatty acids pair up with sodium (or potassium) to become soap, and the glycerol is set free as glycerin. That reaction is saponification.
The soap molecule that comes out of it has a split personality. One end loves water and the other end loves oil. That's how soap grabs onto grease and dirt and lets water carry them away, and we explain it in more detail in how does soap work.
The glycerin matters too. It's a humectant, which means it draws moisture from the air, and it's part of why a good handmade bar can leave skin feeling soft rather than tight. In handmade soap, the glycerin stays in the bar.
Superfat, the little bit of extra oil
Most soapmakers use slightly more oil than the lye can turn into soap. That extra is called the superfat, and it's usually around 5%. It's a safety margin, so there's never leftover lye, and it gives the bar a more conditioning feel. We go deeper in what is superfat in soap making.
Four ways soap gets made
The ingredients are the same, but there's more than one way to put them together.
- Cold process. Oils and lye are mixed at fairly low temperatures, poured into molds and left to saponify on their own, then cured for several weeks. It's the most common handmade method, and the one we use. Here's more on cold process soap making.
- Hot process. The same ingredients are cooked so the reaction finishes in hours instead of days. The bars look more rustic and are usable sooner.
- Melt and pour. A ready-made soap base, already saponified by a manufacturer, is melted down, scented and poured. It's how most clear glycerin soaps are made, and it's a great way to start, since you never handle lye.
- Industrial. Big manufacturers saponify fats in huge batches, dry the soap into pellets, then mill and press the pellets into bars with additives.
Is soap made with chemicals?
Everything is made of chemicals, water included, so the honest answer is yes. A better question is whether the ingredient list is short and makes sense to you. A true soap needs only fat, lye and water. Every ingredient after that is there for scent, color, texture, shelf life or performance in hard water. Some people like those extras, and some prefer a bar with as few as possible. Reading the label is the only way to know which you're getting.
It also helps to know that "natural" has no legal definition for soap in the US. A bar can say natural and still contain plenty of additives, while a bar that never uses the word can be very simple. The ingredient list tells you far more than the front of the box.
What else goes into soap?
Once you have the three basics, everything else is a choice. Here are the most common extras.
- Fragrance. Essential oils are distilled from plants. Fragrance oils are blended scents, and they're how soapmakers get notes like champagne, black raspberry or bourbon that no plant can give.
- Color. Micas, oxides and pigments, or natural colorants like clays, spices and roots. We wrote a guide on coloring soap naturally.
- Hardeners. Sodium lactate, a salt, helps a bar firm up and last longer in the shower.
- Lather and feel. Silk, sugar, honey and milks can make lather richer or silkier.
- Texture. Oatmeal, coffee grounds, poppy seeds and similar ingredients give a gentle scrub. Read about oatmeal soap and honey soap.
- Clays and charcoal. For color and a smooth, slippery feel.
What's in store-bought soap?
Big-brand bars start the same way, with fats and lye, but the label reads differently because ingredients are listed by their chemical names after saponification. Here's a quick decoder.
| On the label | What it is |
|---|---|
| Sodium tallowate | Soap made from beef tallow |
| Sodium palmate | Soap made from palm oil |
| Sodium cocoate | Soap made from coconut oil |
| Sodium olivate | Soap made from olive oil |
| Sodium palm kernelate | Soap made from palm kernel oil |
| Tetrasodium EDTA, etidronic acid | Additives that help soap work in hard water and keep it stable on the shelf |
| Titanium dioxide | A white pigment |
Then there are bars that aren't soap at all. Many popular "beauty bars" and "body bars" are synthetic detergent bars, or syndets, made mostly with lab-made cleansers such as sodium lauroyl isethionate instead of saponified oils. Dove is the best-known example. Find out more in is Dove real soap. Neither kind is wrong. If the front of the box avoids the word "soap," though, that's usually your clue.
What is liquid soap made of?
True liquid soap is made the same way as bar soap, with potassium hydroxide instead of sodium hydroxide, which keeps it soft enough to dissolve in water. Liquid castile soap is the classic example. Most hand soaps and body washes at the store, however, are detergent-based rather than true soap. That's why they can lather so easily in any water and come in such a range of thicknesses and scents.
Is soap made from animal fat?
It used to be, almost always. Before plant oils were cheap and easy to ship, soap was made from tallow and lard, usually with lye from wood ashes. Plenty of soap is still made from animal fats today, especially big-brand bars. If you see sodium tallowate or sodium lardate on a label, the bar contains animal fat. Our soaps are made from plant oils.
Plant oils alone don't make a bar vegan, though. Some soaps include honey, milk, beeswax or silk. If that matters to you, read the whole ingredient list, not just the oils.
A very short history
People have been making soap from fat and alkali for nearly 5,000 years. Babylonian clay cylinders from around 2800 BCE held a soap-like substance, and a Babylonian tablet from around 2200 BCE records one of the oldest known soap recipes, made from water, alkali and cassia oil. Later, soapmakers in Aleppo, then Spain's Castile region and France's Marseille, became famous for olive oil soaps. By the 1800s, cheaper lye made soap an everyday product. The basic recipe barely changed along the way. For the whole story, read when was soap invented.
What's in our soap
We keep ours close to the basics. Our traditional bars are made with organic coconut, olive, palm and sunflower oils, plus phthalate-free fragrance, colorant, sodium lactate to help the bar last, and a little tussah silk for a silkier lather. Our castile bars are made with 100% organic olive oil, with no sodium lactate and no silk. The plain Castile Soap has nothing added for scent or color. Every ingredient is printed on the label.
Want to see the whole process? Our beginner's guide shows you how to make soap at home, with links to our free lye calculator. Or skip the stovetop and browse the soap shelf.