A Guide on Stearic Acid in Soap + 15 Oils With High Stearic Content

If you’ve ever made a batch of soap that turned out softer than expected, one reason could be that there wasn’t enough stearic acid in the recipe. Stearic acid in soap helps to create a harder bar of soap with stable, creamy lather. You can bump up the stearic acid content by using certain oils, fats, and butters such as hydrogenated soybean oil, kokum butter, and illipe butter to name a few examples.

Or, you could also add a tiny amount of pure stearic acid to your soap recipe. If you’re tired of having soft bars of soap that melt away, let’s look at what exactly stearic acid does in soap, along with tips on using it.

Let’s get started!

A quick overview of fatty acids in soap

Fatty acids are components of soap that help give the finished product its unique properties. Every kind of oil, fat, or butter has its own distinct fatty acid profile.

As a soapmaker, once you get familiar with fatty acid profiles of the main soap making base oils, you can determine the type of soap you’ll end up with. You can choose to make one that’s highly cleansing, for example, or one that’s gentler on the skin.

Crafting the perfect bar of soap often involves experimenting with a blend of oils, fats, and butters to achieve a bar of soap that’s neither too hard, nor too soft, but just right.

We categorize fatty acids in soap into two groups: saturated or unsaturated.

Saturated fatty acids

A good indicator that a fat is saturated is if it’s solid at room temperature (like coconut oil and palm oil). If you’re looking to make an extra firm bar of soap, saturated fats like stearic acid in soap are great to use as their molecular structures allow them to stack together neatly.

If your soap recipe contains a high saturated fatty acid composition, you’ll make hard bars of soap with powerful cleansing properties and strong lather.¹

Here are the four saturated fatty acids commonly found in soap:

Lauric acid
Myristic acid
Palmitic acid
Stearic acid

Unsaturated fatty acids

In contrast, most unsaturated fatty acids are liquid at room temperature. Examples include avocado oil, olive oil, safflower oil, and soybean oil.

If your soap recipe contains a high unsaturated fatty acid composition, you’ll get bars of soap that are softer, and more moisturizing. Unsaturated fats have less cleansing power. They produce a milder, creamy lather that’s gentle on the skin.¹

Here are the four main types of unsaturated fatty acids:

Ricinoleic acid
Oleic acid
Linoleic acid
Linolenic acid

👉 Check out our article for more details about fatty acids in vegetable oils.

What exactly is stearic acid?

Stearic acid is a type of long-chain saturated fatty acid with 18-carbon chain (which is why it’s also known as Octadecanoic Acid). You’ll find this naturally occurring fatty acid in both animal fats (lard and tallow) and vegetable oils and butters (coconut oil and palm oil). It’s often a mixed triglyceride with other long-chain fatty acids, and is an ester of a fatty alcohol.²

The word stearic or stearate comes from the Greek work stéar, which means tallow.³ Sodium stearate is the fatty acid salt you’ll find in soaps made using sodium hydroxide lye.

You’ll find that stearic acid is used for many commercial applications: it’s a main component of shaving creams; acts as a thickener and stabilizer in cosmetics, skincare, and other household items; improves viscosity; and acts as a lubricant for industrial purposes.³

At room temperature, stearic acid has no color and is a waxy solid that’s practically insoluble in water.

The formula for stearic acid is: C₁₇H₃₅COOH

Here’s the chemical structure of stearic acid:

WikiCommons_stearic acid in soap, stearic acid — Stearic acid.
*Credit: Wiki Commons*

Note: Most stearic acid you’ll find from soap suppliers is derived from palm oil. (We know that not everyone is a fan of palm oil because of its link to environmental issues.) It’s made through the process of hydrolysis and then distilled and pressed. Stearic acid produced in this way is considered vegan.

What does stearic acid do in DIY soap and other personal care products?

If you’re making homemade soaps. lotions, and candles, here’s what stearic acid does:

Hardens bar soap (cold process, hot process, and melt and pour). Your soaps will release from the mold easier.
Provides a more stable and creamy lather in bar soap.
Emulsifies and thickens lotions, creams, body scrubs, and liquid body washes. You’ll find you won’t need to shake your homemade liquid lotions to mix them before use.
Hardens homemade candles and bumps up the melting point.

15 Soap making oils high in stearic acid

Want to bump up the stearic acid in your soap batch? Consider using one or more of these soap making fats.

While fully hydrogenated soybean oil (aka soy wax) contains the highest levels of naturally occurring stearic acid to my knowledge, it can be a bit tricky to work with. You’ll need to soap at higher temperatures and ensure the wax is fully melted to avoid getting stearic spots.

Many people find that incorporating a butter (or a combination of butters) is an easier way to boost the stearic acid composition in bar soaps.

Tip: When formulating your cold process or hot process soap recipe, a good guideline is to keep the stearic acid content anywhere from 5 to 15 percent. This should provide a reasonably hard bar of soap.

Here are a 15 oils, fats, and butters that contain high to moderate levels of stearic fatty acids.⁴ You’ll notice there are many butters on this list (some with names that I won’t even pretend I know how to pronounce).

123RF_Stearic acid in soap, Soy shortening — Hydrogenated soybean oil (aka soy wax) contains surprisingly highly amounts of stearic acid.
*Credit: 123RF.com*

Soybean oil, fully hydrogenated (aka soy wax): 87 percent
Kokum butter: 56 percent
Illipe butter: 45 percent
Kpangnan butter: 44 percent
Sal butter: 44 percent
Mango seed butter: 42 percent
Shea butter: 40 percent
Cupuacu butter: 35 percent
Cocoa butter: 33 percent
Ucuuba butter: 31 percent
Tallow (goat): 30 percent
Mango seed oil: 27 percent
Tallow (deer): 24 percent
Tallow (beef): 22 percent
Mowrah butter: 22 percent

How much stearic acid to add to cold process or hot process soap

When using store bought stearic acid, less is more. Start off low at around 0.5 percent (of the total oils) in cold process or hot process soap making. You can bump it up to a max of 1–2 percent of the recipe.

Adding too much may cause false trace.

Tips on working with stearic acid in soap

Working with stearic acid in soap is tricky. Stearic acid reacts quickly sometimes producing false trace. It also has a fairly high melting point which requires you to soap at higher temperatures.

Note: The melting point of stearic acid is 156.7 degrees Fahrenheit (69.3 degrees Celsius).

Here are a few tips on working with this finicky additive.

Keep it hot (or at least warm): Soaping at higher temperatures ensures you avoid stearic spots (tiny white dots) in your finished product. As stearic acid has a higher melting point, it’s best to keep your oils around 120 degrees Fahrenheit (49 degrees Celsius) before adding the stearic acid.
Keep mixing: Stearic acid has developed a reputation for tricking soapers into believing they have reached trace. This false trace can be overcome by simply stirring some more. Don’t believe it when your soap batter instantly reaches trace. So, alternate using an immersion blender and manually mixing to stir, stir, and then stir some more.
Add last: Try adding stearic acid to the combined lye mixture and oils last. This buys you some more time before things stiffen up.

Author: Josh Tesolin

Josh is co-founder of RusticWise. When he’s not tinkering in the garden, or fixing something around the house, you can find him working on a vast array of random side projects.