Stearic is a saturated fatty acid that contributes hardness and stable lather in soap making, similar to palmitic acid, except that it has a longer carbon chain. A good amount of butters contain high amounts of stearic acid, including Kokum, Illipe, Sal, Mango, and Shea butters.
A commonly used oil that contains a gigantic amount of stearic acid (more than any butter) is hydrogenated soybean oil (sometimes referred to as soy wax or soy shortening).
According to industry reports, the average percentage of stearic acid in the favourite soap recipes of soap makers is round 7 percent. The two super high percentages of stearic acid completely bumped the average out of proportion; most recipes tend to clock in at 3 percent to 8 percent stearic acid. Some recipes also contain stearic acid at 0.5 percent to 1 percent of the total soap formula
However, when added to soap formulations, Stearic Acid derivatives function as thickeners that help to harden the formulas into solids and that help to eliminate the thin and runny feeling of watered-down soaps. Their surfactant action helps reduce the surface tension of oils, which makes it easier for oil and water molecules to mix well.
In this way, Stearic Acid strives to make sure that emulsions do not separate into isolated layers of water and oil. This helps enhance a product’s effectiveness as well as its shelf life. This also means that final products with Stearic Acid do not need to be shaken as vigorously before they are used.
While soaps can be made using a variety of fatty acids, stearic acid is one of the most popular. Stearic acid salts made with sodium, potassium, calcium, strontium, barium, and magnesium are used in a variety of applications.
Sodium stearate is the most common type of soap and has been used extensively in cleansing for personal care in bar soaps. Potassium stearate is softer and more water soluble and has been used in water solutions for hard surface cleaning.
Even with their widespread use, stearic acid soaps do have certain drawbacks. First, it is hard to prepare concentrated solutions of these soaps because they are only marginally soluble in water. In addition, they can react with minerals present in hard water and form insoluble salts such as calcium stearate. These insoluble salts are responsible for bathtub ring and can leave undesirable film on hair, skin, and clothing.
Benefits of Using Stearic Acid in Soap Making
According to the Skin Store website, stearic acid is a very common additive used in the manufacturing of more than 3,200 skin, soap and hair care products, such as soaps, shampoos and household cleaners. Below are the benefits of stearic acid in soaps;
1. Natural Skin Cleanser and Lubricant
Soaps with stearic acid have a higher chance of actually stripping the skin of dirt, oil, and grease. Your daily post-makeup routine will become much easier, and much more effective. However, more than that, stearic acid is a secret weapon when it comes to facial moisturisers. It can lock in moisture by protecting the skin’s surface against water loss and creating a waxy protective barrier.
When you are using a product that contains stearic acid, you don’t have to shake it vigorously before you use it; the presence of stearic acid in a product helps to extend not only its effectiveness, but also its shelf life.
It is the stearic acid that works to dislodge the grime, sweat and extra oil from your hair and skin when you apply shampoo, soap, face wash or body wash. This cleansing feature of stearic acid is also the reason it is used in detergent powders and liquids – it does the work of cleaning your clothes.
2. Surfactant Agent
A surfactant, or surface active agent, reduces tension between two substances. One of the most important benefits of stearic acid is its ability to help make water and oil mix together more easily in products. Note that it is fairly insoluble in water but becomes somewhat soluble in alcohol.
More importantly, it helps lower the surface tension of oil, allowing it to combine better with water so together the two can be used to thoroughly wash anyway microbes from skin, hair, etc. As a surfactant, it can also attract oil, dirt and other impurities that accumulate on your skin and on other surfaces.
3. Natural Emulsifier
Stearic acid is used to help prevent ingredients in different types of soaps / formulas from separating. It is used to thicken/harden formulas and bind together ingredients so they don’t wind up separating into liquid and oily layers. This prolongs how long soaps stay stable and usable.
You’ll also find stearic acid in supplements, such as magnesium stearate, for this reason. It is added to keep the solid ingredients from falling apart and aid in the proper release of active ingredient after someone swallows the supplement.
4. Effective facial moisturizer
Stearic acid helps facial moisturizers hold more water in proportion to oil than other facial moisturizers. First, this helps the product last longer. With stearic acid in the product, the oil, water, and other ingredients are very unlikely to separate into their individual components.
You won’t ever face the problem of pouring liquid soaps or moisturizer in your hand and watching it come it out in its unblended state. Additionally, the water content makes the liquid soap or moisturizer kinder and runnier. The moisturizing oils bind faster to your skin, keeping it moisturized for longer, without sabotaging the natural oil production of your skin.
Conclusion
Stearic acid is considered safe for most people and easy to tolerate, even for aged skin and when worn in the sun. However, there’s always a chance that someone can have sensitivity, so start by using stearic acid – containing products sparingly at first to test your reaction. Stearic acid is generally not meant to be consumed, and is for exclusive external use.
If consumed, it can cause chemical pneumonitis. People with especially sensitive respiratory systems, high vulnerability to allergies, pregnant and nursing mothers, and so on, should take special care if they have to handle stearic acid in the raw form, and are advised to seek medical consultation beforehand. Raw stearic acid should not be left in places easily accessible to children under the age of 8.