Don’t you also like it if a soap feels sumptuous almost velvety on your skin? Or when your skin feels soft and supple after applying a moisturiser? Or the rich and thick foam of a shaving cream giving your skin a smooth and nick-less vibe? That’s all thanks to a single ingredient: Stearic acid.
Most probably, you’ve already encountered stearic acid in your daily life: When you light a candle, when you use a detergent to clean, when you pop chewing gum in your mouth, when you store leftover food in a plastic container, when you play cards… and of course when you apply makeup or go through your skin care routine.
Not Your Typical Acid
Stearic acid stearic has a PH level of about 6. Even though technically, it is classified as an acid, it’s not at all like the bond-dissolving AHAs and BHAs – your typical chemical exfoliants.
Stearic is only slightly less acidic than your skin (should be or) is and slightly more acidic than water which is normally at PH 7. Despite having acid in the name, fatty acids are not tissue-dissolving but the building blocks for fats and oils.
It’s a fatty acid with a long hydrocarbon chain. It’s one of the most common long-chain fatty acids. As such, it occurs naturally in the stratum corneum (upper layer of our skin), animal tissues, and many plants. Generally, it’s more abundant in animal fat with the exceptions being cocoa and shea butter.
Sometimes, it also goes by the name octadecanoic acid and you may also see it listed as
- Century 1240
- Cetylacetic acid
- Emersol 120 or 132 or 150
- Formula 300
- Glycon DP
Stearic acid is a wax-like colourless solid with a light and for some noses unpleasant odour. It has a water-loving hydrophilic head and an oil-loving hydrophobic tail. This property allows it to function as a surfactant and at the same time as an emulsifier, and thickener.
As a surfactant, it can make formulations stick to both water and oil or grease and then rinse them away with water. That’s the basic description of any soap, cleanser, or detergent.
Normally, water and oil don’t mix. When you shake water and oil tougher, you see a dispersion of oil droplets in water or water droplets in oil. But when you let the dispersion stand a while, the oil and water separate. As an emulsifier, it helps water and oil to stick together – be it a moisturiser, lotion, or whatnot – into a smoother, thicker blend.
Basically, without stearic acid, things like soaps, candles, plastics, and oil pastels can’t hold their shape. Soap wouldn’t be so easy to use without its bar shape and oil pastels would be running everywhere.
History
The word “stearic” come from “stear” Greek for fats that you get as a by-product when you cook meats – tallow in English. Being a component of vegetable and animal oils and fats, stearic acid is one of the most common fatty acids. This also makes it one of the oldest cosmetic ingredient.
Uses in skin care formulations
Stearic acid is mainly used to stabilise a formulation.
Emulsifier
As an emulsifier, its role is to improve the texture, shelf life, and scent of a product giving it a smooth, satiny feel.
It helps a product to last longer. Without stearic acid, the oil, water, and other ingredients split into their own individual components. When stearic acid is added to the mix, you won’t be greeted with a mess of separated ingredients when you try to scoop out your moisturiser out of its tub.
Thickener
Stearic acid helps to thicken or harden a product. Just think of moisturisers, hand creams, or hair conditioners. These are water-based and thanks to stearic acid, these products aren’t runny but have a nice viscosity so that they’re smooth, creamy, and spreadable.
Surfactant
Stearic acid acts as a mild surfactant. This means it can attract water, oil, and grease so that you can lift any grime away from your skin and hair. It helps to create a lather when mixed with water and gives a rich, satiny feeling.
Skin Benefits
Why does it feel rich, satiny, or velvety on your skin?
Natural moisturising factor
As an important naturally occurring component of stratum corneum lipid, stearic acid is a natural emollient. Since it’s a natural moisturising factor (NMF) it penetrates your skin quickly where it helps to retain moisture. It creates a waxy protective film thereby sealing in water and preventing water loss.
It moisturises and binds oils faster to your skin, keeping it moisturised for longer, without sabotaging the natural oil production of your skin.
Preserve the skin’s natural barrier
The outermost layer of your skin, the stratum corneum, looks a lot like a brick and mortar wall when you look at it under a microscope. The bricks are your dead skin cells (corneocytes) and the mortar is the mix of lipids consisting of ceramides, cholesterol, and fatty acids.
The role of stearic acid as an NMF is to hold together the bricks (corneocytes) and so keep up the wall (your skin’s natural barrier). A functioning skin barrier prevents water loss and any external foreign substances to enter which can cause inflammation and infection.
Natural cleanser
Surfactants or cleaning agents draw water and oil and so lift any grime, bacteria, and makeup from your skin. Regular surfactants can be too harsh and wash away not only dirt but also your skin’s lipids (you know, the mortar from your skin’s natural barrier).
Unlike regular surfactants, stearic acid is gentle. It cleanses but also has softening and refattening qualities. It restores lipids in hair or your skin.
Is it safe
The US FDA classes stearic acid as safe both for consumption when used as a food additive and for topical uses in skin care products. Stearic acid is used in uncountable personal care products because it’s safe and versatile. It’s also found in argan oil which is considered the most expensive oil.
Who should use it
It’s well tolerated by all skin types and works well for most of us. It’s particularly helpful for
- Oily and acne-prone skin since it’s a gentle cleanser yet powerful enough that it can lift excess sebum and other debris from jammed pores
- Sensitive skin and those prone to allergies since its an NMF, it strengthens your skin barrier, and it’s also less likely to trigger any reaction
- Dry or mature skin since it’s an excellent moisturiser that helps oils bind faster to your skin.
Closing words
There’s a fair chance you’re already using stearic acid as it’s a very common ingredient in creams, shampoos, and soaps. If you specifically want to add it to your routine, you may want to add it as plant oil or butter:
- Candlenut oil
- Cocoa butter
- Coconut oil
- Mango butter
- Marula oil
- Neem
- Palm oil
- Rice bran oil
- Shea butter
- Tamanu oil
