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.

you are viewing a single comment's thread
view the rest of the comments
[–] 69 points 3 months ago (20 children)

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%).

  • source
  • hideshow 20 child comments
  • [–] [S] 27 points 3 months ago (7 children)

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

    Damn.

  • source
  • parent
  • hideshow 7 child comments
  • [–] 72 points 3 months 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.

  • source
  • parent
  • [–] 6 points 3 months ago (2 children)

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

  • source
  • parent
  • hideshow 2 child comments
  • [–] 12 points 3 months ago (1 child)

    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.

  • source
  • parent
  • hideshow 1 child comment
  • [–] 1 point 3 months ago (8 children)

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

    but in practice the second layer won't be as thick...

  • source
  • parent
  • hideshow 8 child comments
  • [–] 8 points 3 months ago (7 children)

    Depends how you apply it. I smear it on like butter.

  • source
  • parent
  • hideshow 7 child comments
  • [–] 3 points 3 months ago (3 children)

    Careful of sunscreen stains. I apply 2 thin layers under air conditioning to minimize the moisture and allow it to fully dry.

  • source
  • parent
  • hideshow 3 child comments