stearic acid

CAS No-57-11-4

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.

Softens the skin: 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.
Helps decrease the signs of aging: As it strengthens the skin barrier, stearic acid protects against water loss and even helps decrease the signs of aging, says Hu.

Can be tolerated by sensitive skin: Stearic acid is 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.
Helps cleanse the skin: 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.
Doesn’t strip the skin’s natural oils: 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.

Helps products apply more evenly: 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.
Stabilizes products: 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.