Originally posted by: notfred
Originally posted by: BigJ
Originally posted by: Special K
Originally posted by: notfred
I don't get the purpose of ultra-high SPF sunscreen. The idea is that the amount of sun expusure you get is 1/n what you would get with no protection, where n is the SPF of the sunscreen.
I looked it up. A white cotton t-shirt is essentially SPF 5. Yes, 5. All those super-high SPF rated things are ridiculous overkill.
If you can stay out in the sun for an hour without burning with no sunscreen, you can stay out for an entire day with SPF 15.
I thought the strengths of all sunscreens were the same, and the SPF only referred to the duration of the protection? For example, suppose you could normally be out in the sun for 10 minutes before starting to burn without wearing any sunscreen. An SPF 10 sunscreen will theoretically allow you to say out for 100 minutes before starting to burn, and an SPF 20 would give you 200 minutes.
Bingo.
However long you can stay out in the sun without sunscreen, is what you multiply the SPF by to get how long you can stay out in the sun with that sunscreen.
That is true *because* of what I said. If you can stay out for 1 hour normally, and you put on SPF 15 sunscreen, you're now getting 1/15th the amount of sun you were getting before. You can stay out for 15 hours before you burn.
What Special K said is entirely false, even though it's similar to what you said.