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.

  • slazer2au
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    5 days ago

    SPF rating is subjective at best and not a regulated term in many countries.

    Australia is a place where it is a regulated term and a test by Choice showed that 16 of 20 products failed their rating and several have since been recalled.
    https://www.choice.com.au/health-and-body/beauty-and-personal-care/skin-care-and-cosmetics/articles/sunscreen-test

    Back to your original question which is answered in the article

    In percentage figures that means the difference between, say, an SPF 50 sunscreen and an SPF 30 sunscreen is less impactful than you might assume. An SPF of 50 protects you from all but 1/50th of UV rays (98%), while sunscreen with an SPF of 30 protects you from all but 1/30th of UV rays (96.7%).

    • MaroonOP
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      5 days ago

      No way! So like I’d be be paying exponentially more for an additional 0.6% if I brought the SPF75!

      Damn.

      • ✺roguetrick✺
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        5 days ago

        Yeah but any power gamer loves this math because that 0.6% is still a nearly 30 percent damage reduction compared to the lower grade sun armor so you’ll be stomping those pubs that don’t persue it.

      • protist@retrofed.com
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        5 days ago

        Does higher SPF cost more where you live? I just bought both 50 and 100 and they were the same price

      • slazer2au
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        5 days ago

        Yep. Welcome to capitalism, where the bigger made up number actually mean very little in real terms.

        • AmidFuror@fedia.io
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          5 days ago

          Everyone knows that Societ sunscreen was the pinnacle of effectiveness and issued according to need.

    • Sheridan
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      5 days ago

      I looked up sunscreen recommendations on Consumer Reports and virtually every sunscreen didn’t perform as well as advertised in CR’s lab tests. CR’s top rated sunscreens all happen to be marketed for kids/babies oddly enough.

      • blarghly
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        5 days ago

        You get sunburned: “oh, silly me, I must have forgot to reapply”

        Your baby gets sunburned and spends the next 72 hours crying: “I will murder the CEO of Johnson & Johnson”

    • lemonhead2
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      5 days ago

      so if u do two spf 50 layers u should get spf 2500.

      but in practice the second layer won’t be as thick…