Mixing sunscreen with foundation

[CutesyUserName]

I use Biore WE over Cerave AM moisturiser (Factor 25). When I need to wear makeup, I use EL Double Wear and sometimes like to mix it with a little moisturiser to make it a bit lighter. As we head into summer (joke) is there any reason I shouldn't use the Biore to do this instead, given I already have a proper layer underneath? I want all the sun protection I can get.

I don't think layering different SPF products (or the same product twice) means you get a higher level of protection. You just need to make sure you apply the highest strength product really well in the first place. So, your moisturiser having factor 25 is irrelevant, given the Biore is (iirc) factor 50.

Layering sunscreen products does not really make much of a difference - if you have correctly applied (meaning applied enough product) SPF20 and SPF50, then the level of protection is SPF50.
You will not get SPF70 by layering the two products.

In order to get the highest level of protection of your SPF product, you need to use around a quarter teaspoon for your face. Using less means you will get a lower level of protection than stated on the bottle.
This goes for any SPF product; foundation, BB cream, moisturiser, proper SPF and so on. It has to do with how it is tested, two milligrams of sunscreen per square centimeter of skin should give you the protection level stated on the bottle.
Most people do not apply that much foundation, and I doubt we even apply that much moisturiser.

For the body (average 70kg man used as an example), it's around a shot glass (~28ml). 2 tablespoons (30ml) should be enough for the face and the body.

If you dilute Biore Watery Essence (SPF50) with foundation, and use less than the quarter teaspoon of the Biore product in total, then you do not get the SPF50 protection stated on the bottle.
Generally, the average application of SPF30 really only gives us SPF10-12 - because we don't use enough product.
So if you use a couple of drops of Biore with the foundation, you probably barely get any significant SPF from that alone.

Also, as far as I'm aware, if layering SPF, you need to be careful as some products contain different SPF ingredients (octinoxate and avobenzone) and they can degrade/break each other down, meaning the SPF will not work correctly, so should be reapplied more frequently.

Sorry about the long post :)

dermatologist s say that the facial moisturisers do very little.it is now seven weeks to peak uv so wear real sunscreen.

Thanks for the replies, all. I would always apply my sunscreen first, then on days with makeup add this over the top, diluted with some more sunscreen. I use SS liberally, so easily getting more than quarter of a teaspoon. I think I get that much on one quarter of my face.

I really just wondered if there was any good reason not to use SS to dilute foundation when I needed to instead of moisturiser. I didn't think there would be, but thought it best to ask others first. Thanks again.

Now, let's hope for some sun!