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.

  • Lasherz@lemmy.world
    21·
    8 days ago

    If you’ve ever used a UV camera it’s pretty clear that much like lotion not absorbing after a certain point, there’s a limit to how dark your skin gets with a given sunscreen. Also that there’s a massive difference between brands and formulas. I had some photos I took with one but can’t find them. If I do later I’ll update.

    Searched but couldn’t find them. Did find a conversation though where I used it to show most cars in a parking lot have UV blocking windshields but every other window is transparent unless they have tint

    • Alcoholicorn@mander.xyz
      1·
      8 days ago

      How did the Vaseline spf50 work? Thats what I use on my body since it seems the most water-resistant, but I still get pretty dark. Did you test face sunscreens?

      • Lasherz@lemmy.world
        6·
        8 days ago

        I wouldn’t say our tests were perfect, just smearing it on cardboard, but we did test like 10 different ones. Few things were obvious, like that the coral reef destroying ingredient ones were more effective than the more eco ones, and that banana boat kinda sucked. Neutrogena was good and even their 15 spf was just about as dark as their 30. I think coppertone was worse than banana boat but I’d wanna retest before I recommend any of them though. My memory isn’t that good, I just remember relief that Neutrogena was good because it’s what I’ve been using.

        https://a.aliexpress.com/_mq8c3YB this is the one I have, although I bought it when it was 50 bucks and a quick glance shows most over 100 now.