Whether or not you mix your foundation with your sunscreen, or you apply a layer of sunscreen before putting on foundation, the foundation will influence the total amount of UV protection.
If you’re mixing the two, the amount of protection from the sunscreen alone will be proportionally weakened depending on the amount of foundation used and the level of protection provided by the foundation itself. So for example, take my favorite daytime foundation (Smashbox Studio Skin SPF 15, which contains 4.7% titanium dioxide (TiO2)); and my favorite sunscreen (EltaMD UV Pure SPF 47, which contains 10% zinc oxide (ZnO) and 5.5% TiO2). I mix roughly three parts of sunscreen to 1 part of foundation. This calculation would yield an average UV filter content of: Mixture = ((10% + 10% + 10% +0%) ZnO)/(3 + 1) + ((5.5% + 5.5% + 5.5%+ 4.7%) TiO2)/(3 + 1) Mixture = (7.5% ZnO) + (5.3% TiO2)Using the sunscreen simulator provided by BASF at an application amount of the standard 2.0 mg/cm^2, the resulting Mixture would yield an SPF rating of about 15 and a UVA-PF rating of about 7.0. (I usually apply more than the recommended 2.0 mg/cm^2). Now, if we were to mix in a foundation without any UV filters, the resulting mixture (7.5% ZnO and 4.125% TiO2) would have an SPF rating of about 10 and a UVA-PF rating of about 6.0. While the numbers, especially the SPF ratings, appear to be quite different; in reality, is it THAT different? Not really. An SPF of 15 blocks about 93.5% of UVB rays, while an SPF of 10 blocks about 90% of UVB rays (difference of 3.5%). Similarly, a UVA-PF rating of 7 blocks about 86% of UVA rays, while an UVA-PF rating of 6 blocks about 83% of UVA rays (difference of 3%). As you can see, the difference between using a foundation with or without SPF does not make a significant difference in the overall level of UV protection. Is it better than nothing? Yes, which is why I choose to mix a foundation that provides “decent” UV protection into my sunscreen. ***Keep in mind that this model was simply an abstract way to illustrate a point. In reality, calculating the levels of UV protection is not that simple. There are many factors that can influence a sunscreen’s capacity to protect, as demonstrated in the sunscreen series. However, this is the most accurate way for the average consumer to get an idea of how much relative UV protection a sunscreen provides. For more details into why and how to mix “sunscreens,” check out this post.
Now, if you choose to apply sunscreen before you apply foundation, the sunscreen will still be negatively affected by the foundation. Here’s why: application. No matter if you use your fingers, a sponge, or a brush, any manual type of application will affect the layer of sunscreen. Because no matter how careful you are, the application method will either blend some of the sunscreen and foundation together, remove some of the sunscreen (via swiping, patting, or buffing motions), or both. And because no one has such muscle control as to apply an even amount of pressure throughout the entire application process, some areas will have more protection, while others will have less. Therefore, it is my recommendation to simply mix your sunscreen with foundation, rather than layering the two. You may be getting slightly less protection by mixing, but at least you’re getting EVEN protection, rather than a little here and a lot there. ***The only exceptions to this rule are if you were to use an airbrush foundation system, or if the "foundation" or tinted moisturizer/BB cream that you're layering with provides roughly equal or more protection than the sunscreen itself; slightly less works fine as well. If these apply to you, then layer away! ***Also, this mixing method is recommended over the layering method only if your sunscreen is inorganic-based, meaning that TiO2 and/or ZnO are the primary UV protectors. As demonstrated in the above-linked sunscreen series, which detailed why and how inorganic sunscreens are preferred over organic ones, the "ideal" sunscreen IS an inorganic one. However, if you are using an organic sunscreen, layering would be preferred over mixing due to the fact that, as indicated multiple times before, "organic UV filters are more tempermental and more easily manipulated by the base ingredients and UV filters." Ultimately however, the most important thing to do is to apply enough sunscreen so that the subsequent steps like foundation and powder do not significantly affect the overall level of protection. I always try to aim for 3.0 mg/cm^2!
Makeup products with UV filters can be useful. It just depends on what type of makeup item contains them. My recommendations for the ideal routine are as follows:
I hope that was informational, and feel free to share your thoughts down below! What are YOUR favorite makeup products with SPF?