‘I’m a Cosmetic Chemist and I’m Begging You Not To Mix Your SPF and Moisturizer’

Slathering on SPF on a daily basis can seem like a chore, especially if you don’t have one that you particularly love. It’s the grand finale to one’s skin-care routine and you certainly don’t want to skimp on the protection. But as it turns out, SPF is a bit more complicated than we think. The FDA won’t tell you this but cosmetic chemists and dermatologists are urging SPF users to avoid mixing it with other skin-care products, specifically there are reasons why you shouldn’t mix SPF with moisturizer.

Why you shouldn’t mix SPF with moisturizer

Everyone is always looking for ways to cut down the length of their routines, but let it be known that this “hack” is simply not it.

“The concentration of physical and chemical filters is carefully determined during the formulation and testing process [of SPF],” says Cara Bondi, a cosmetic chemist with over 22 years of experience at major beauty companies like Seventh Generation, Tata Harper, Ursa Major, and Sol de Janeiro.

When you mix your SPF with other products, she says, you're basically diluting it. “You alter the total concentration of the filters and the homogeneity of the mixture, which results in less overall potency and an irregular distribution of UV filters throughout the mixture you've made,” Bondi explains.

What’s more: “SPF is a tightly regulated category where the finished products have to undergo an exact testing protocol approved by the FDA to ensure that it provides the UV protection stated on the label. Any alteration can affect the amount of UV rays it filters through, as well as the concentration,” says Krupa Koestline, cosmetic chemist and founder of KKT Consultants.

But what about SPF moisturizers?

Mixing in anything, be it moisturizer, foundation, or any other product, dilutes the level of protection and UV protection is no longer guaranteed within your SPF. But if your SPF is formulated and marketed to be a 2-in-1 SPF moisturizer that is okay as that formula was approved by the FDA.

“Moisturizers with SPF are formulated as SPF products, so the formulation and testing process is the same as if it were a primary SPF, it is in no way the same as mixing two products together and diluting your SPF,” Bondi explains.

In the past, this category tended to have lower SPF factors to favor better application and absorption, according to Bondi. “However, due to innovation in raw materials, now there are many moisturizers with SPF values over 30 that are nearly indistinguishable from a non-SPF moisturizer, so the compromise is not as prominent as it once was,” she adds.

Are there specific ingredients that ruin the efficacy of SPF?

No, there isn’t a particular ingredient or family of ingredients to blame for ruining the strength of SPF should they be mixed together. Instead, Krupa suggests you should think of it like lemonade. If you add water to it, you’ll dilute it and it won’t be as strong. In this case, the moisturizer or foundation is water and is diluting the SPF.

“One important note,” says Koestline, “SPF testing requires the application of two milligrams per square centimeter (mg/cm 2). You are likely applying about that much moisturizer on your skin with about ¼ of a teaspoon.”

The bottom line? Layering your skin-care products is key if you want to stay as protected as possible. Or, find a 2-in-1 product if you think it suits your routine and lifestyle better. SPF is all about preference and once you find one you love, it won’t feel like applying it is a chore.