These creams have some chemical that blocks the UV with some capacity, say a factor of 50. Why can’t I apply two layers of this cream to now get a 100 factor equivalent protection?

I asked the chemist at the store and they said it’s not how it works and that the highest protection factor they have is 75 (which was super expensive).

What gives?

Edit: Thank you for those super informative answers.

  • ramble81@lemmy.zip
    16·
    6 days ago

    Think of the visible spectrum of light. If you were to mix a 30% shade of white with a 30% shade of white, you get…. A 30% shade of white.

    Now just switch that coloring to the UV end of the spectrum and it’s the same thing. You’re not layering it realistically, you’re basically just mixing it together and the result is still the same “color” you started with.