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Stearic acid—you may not have heard of it, but it's probably in at least one of the skincare products you're currently using. Stearic acid is by no means an ingredient that should raise any cause for concern. In fact, it's a unicorn in the skincare world in that it's often used for formulation purposes but also delivers some legitimate benefits for your skin, as well. That's no small feat when you consider that skincare ingredients typically fall into either the "active ingredient that does something" or "inert ingredient that's really only being used to formulate the product" categories. Ahead, Los Angeles-based cosmetic chemist and founder of Perfect Image David Petrillo, New York City dermatologist and Assistant Professor of Dermatology at the Mount Sinai School of Medicine Diane Madfes, M.D., and cosmetic scientist Shuting Hu, formulator and founder of Acaderma, explain all there is to know about this somewhat unknown ingredient.
Meet the Expert
Type of ingredient: Emollient, surfactant, and emulsifier
Main benefits: Softens and smooths the skin's surface while also helping to maintain the skin barrier. It also works as a surfactant, though it is often used as an emulsifier to thicken products and improve their texture, says Petrillo.
Who should use it: Stearic acid is extremely well-tolerated and something that pretty much anyone can use, though it's an especially great ingredient for those with sensitive, dry skin, points out Madfes.
Works well with: Almost all ingredients, specifically many oils. It's also often paired with more irritating actives to minimize the drying side effects.
Don't use with: According to Petrillo, there are no specific ingredients that stearic acid doesn't work well with.
What Is Stearic Acid?
The name can be somewhat of a misnomer because this isn't the same type of acid as, say, the glycolic or salicylic acids you may be familiar with. "Stearic acid is a saturated, long-chain fatty acid that's found naturally in various animal and plant fats," explains Hu. (Though it's worth mentioning that the stearic acid used in skincare can also be synthetically derived.) Basically, think of it as a moisturizing fat; in fact, it's a natural component in some moisturizing ingredients you may already be using, namely cocoa butter and shea butter, says Madfes.
Benefits of Stearic Acid for Skin
As mentioned, stearic acid is often used purely for product formulation reasons, but it has some specific skincare benefits even on its own.
Is a moisturizing emollient: Moisturizing ingredients typically fall into three categories: humectants, emollients, and occlusives. Stearic acid is an emollient, meaning it works by softening and smoothing the skin. (Other examples of common emollients include jojoba oil, ceramides, and squalane.) In short, this is why it's used to add moisturizing properties to products, explains Madfes.
Bolsters the skin barrier: That being said, stearic acid also does a little bit more than just that. It's an important component of the skin barrier, the outermost layer of the skin responsible for keeping natural moisture locked in and irritants locked out. Think of the skin cells in the barrier as bricks; stearic acid (and other fatty acids), along with things such as cholesterol and ceramides, are the mortar, imperative for keeping those bricks glued together to create a smooth surface with no cracks. As such, stearic acid can help strengthen your skin barrier, protecting against water loss and even decreasing the signs of aging, says Hu. It's also what makes stearic acid a good choice for those with sensitive or irritated skin; Petrillo notes that it can even help reduce the flaking and itchiness associated with psoriasis.
Acts as a surfactant: Here's where things get a little more interesting. Unlike other emollients, stearic acid is unique because it also works as a surfactant—essentially an ingredient that helps cleanse the skin—which is why it's found in many cleansers, notes Madfes. Simply put, "it helps oil-water and dirt bind together and be removed from the surface of the skin more easily," explains Petrillo. But, unlike other surfactants (ahem, sulfates), it doesn't strip your natural oils along with it. Plus, you're simultaneously getting all of those aforementioned moisturizing effects, making it ideal for those looking for a gentle cleanser that won't further dry out or irritate already-compromised skin.
Again, it has to be underscored that stearic acid is primarily used in cosmetic and skin care formulas as an emulsifier, notes Petrillo. Many cosmetic chemists consider using it to give their products a more luxurious feel and to help them apply more evenly, he says. Hu adds that it's what creates that smooth, silky texture we all love, and that it also stabilizes final formulas and keeps them from separating.
Side Effects of Stearic Acid
All of the experts we spoke with agree that stearic acid is a safe ingredient typically well-tolerated by any skin type. That being said, Petrillo points out that any ingredient always has the potential to trigger an allergy or reaction.
How to Use It
You've heard our experts sing the praises of stearic acid, so it may come as a surprise that this actually isn't an ingredient you need to go out and look for. Primarily, stearic acid goes into a product for formulation reasons—those skincare benefits are just a bonus. As mentioned, it's a natural component of other ingredients that you probably seek out, like cocoa and shea butters. If you do want to look for it specifically, you'll typically find it in creams and lotions, as well as face and body cleansers (credit those surfactant properties we talked about). And Madfes points out that it may also crop up in newer retinol oil formulations. Because it's a fatty acid, it mixes well with other lipids (the oils) and also helps counteract the potentially drying and irritating side effects of retinol by strengthening the skin barrier, she explains.
The bottom line: You don't need to search for stearic acid since it's more than likely already in at least some of the skincare products you're using. And that's a good thing, not something to be concerned about.