Ebony asks…Does mixing moisturizer SPF 20 and tinted moisturizer SPF 20 make SPF 40?
The Right Brain responds:
We have the smartest readers in the whole wide world. When this question came up in the Forum, astute reader SarahF came up with this answer:
Common sense chemistry
“…the easiest way of thinking about it is if you took two of the same sized cups of water and put two drops of blue food coloring dye in each cup. The depth of blue color you’d get in each cup would be the same. What color blue would it be if you then mixed your two cups together? The same color blue. In the analogy, the food coloring is like the active ingredients in your sunscreen/moisturizer, and the water is the inactive ingredients.”
We love her common sense explanation. The only thing we’d add is that there MAY be some benefit to using SPF in both products because if you under-apply the first product the second product will help ensure you get enough coverage. In other words using two SPF twenty products won’t give you SPF 40 but it will help ensure you that you apply enough to get to 20. It doesn’t matter what the SPF number on the bottle is if you don’t apply enough to your skin!
The Beauty Brains bottom line
Forum members smart. Not wearing sunscreen dumb.
Image credit: mathsforlaughs.co.uk
{ 5 comments… read them below or add one }
I’m famous!!!! Hi, mom! Hi, Dad! And now, I’d like to take this opportunity to thank my favorite childhood science teacher, with whom I recently reconnected in anticipation of an upcoming reunion for my first school! I sent him this page. He’s brilliant.
And agreed, I like to layer spf products.
@sarah: Be careful. With great power comes great responsibility.
Thanks for the heads up, lol:)
That’s a great analogy! I use a SPF 15 moisturizer and then my powder has SPF 20, so I am good to go! Plus I sit in a office all day, no windows in sight
, so I never have to worry about my SPF protection waning during the day.