SPF Doesn't Stack: Why 30 + 30 Isn't 60
Layering an SPF 30 moisturizer under SPF 30 makeup doesn't get you to SPF 60, and assuming it does can leave you under-protected.
Layering SPF products does not add their numbers together. You effectively get the protection of the single highest-SPF product, and only when it is applied at the correct amount.
Dermatology and skin-cancer education groups note that because most people under-apply, leaning on stacked-SPF makeup steps tends to leave you with less protection than the labels suggest, not more.
Questions we get a lot
If I layer SPF 30 and SPF 30, do I get SPF 60?
No. SPF values do not add together when you layer products. You get roughly the protection of the single highest-SPF product, assuming it is applied at the correct amount.
Does SPF in my makeup count toward my sun protection?
It can contribute, but most people apply far too little makeup to reach the labeled SPF, so it should not be your only line of defense. The Skin Cancer Foundation recommends a dedicated sunscreen layer underneath your makeup.
How much sunscreen should I actually apply?
Dermatologists recommend applying enough to cover all exposed skin generously and reapplying regularly, because under-application is the most common reason real-world protection falls short of the label. The AAD's sunscreen FAQs cover correct usage.
r/MakeupAddiction: 'If my moisturizer is SPF 30 and my foundation is SPF 30, am I getting SPF 60 of protection? My friend swears I am.'