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Simple question about sunscreen

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I know what the SPF number means. Say if I get burned under sunlight without sunscreen in 10 minutes, a SPF of 12 would protect me from the sun for 120 minutes.

I usually apply my SPF 30 (which should offer 5 hours of protection) sunscreen at 6am before I drive off to class, but since the sun doesn't usually shine much until 8am here, would that 2 hours be a complete waste of sunscreen? Would it mean that I have no protection whatsoever after 11am?

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bump again.

here's the thing, I apply the 30 SPF sunscreen at 6am, drive to school and I'm in class by 8am. In this period there isn't much sun anyway. Then I'm usually in class where there isnt any sunlight until around 12pm. So the only time my skin needs protection from the sun is after 12pm. Would my sunscreen still be effective by then?

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the spf number refers to time spent under the sun, not time spent on the skin. so in your example, if you have on spf 12, you can spend 60 minutes in the sun, go inside for a few hours, then spend 60 more minutes in the sun before you start to burn. it's not really that exact, though. the spf number is more of a guideline.

sunscreen does wear off or go away or something over time, especially with sweating and swimming and showering, but this is not related to the spf number. the bottle should say how long it lasts before you need to reapply it. if you're just sitting around in a classroom, it should last longer than normal, unless you're rubbing it off on the chairs and your classmates and such.

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the spf number refers to time spent under the sun, not time spent on the skin. so in your example, if you have on spf 12, you can spend 60 minutes in the sun, go inside for a few hours, then spend 60 more minutes in the sun before you start to burn. it's not really that exact, though. the spf number is more of a guideline.

sunscreen does wear off or go away or something over time, especially with sweating and swimming and showering, but this is not related to the spf number. the bottle should say how long it lasts before you need to reapply it. if you're just sitting around in a classroom, it should last longer than normal, unless you're rubbing it off on the chairs and your classmates and such.

Ahhh many thanks. This is what I was asking about. :)

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oh yeah... the other thing is that once your skin burns, putting more sunblock on won't prevent more burning, no matter what the spf. you have to stay out of the sun for a while and let the sunburn heal.

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oh yeah... the other thing is that once your skin burns, putting more sunblock on won't prevent more burning, no matter what the spf. you have to stay out of the sun for a while and let the sunburn heal.

Hmm I didnt know that. Interesting. I dont really know my 'burn' time, dont plan to find out anyway.

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