Hellobee Boards

30 is good but you'll want to re-apply VERY frequently (like every 2 hours).

Make sure you apply before you get in the sun so it has a chance to soak in. When we were on our beach vacation, I actually lotioned her up in the room while she was naked to make sure I got all the spots without reaching under a swim suit or diaper. I put it on really thick and let it soak in. From there I just reapplied.

Reapplying only helps what sweats off or gets washed off in water, it does not make it last longer. If you take 3 minutes to burn, SPF 30 will delay that thirty times, so 90 minutes to burn. It doesn't matter how thick you put it on or how many times you reapply, you will burn after ninety minutes.

Lightweight long clothing and is a good bet as a physical barrier, as is zinc cream, but it will stay white on the skin. Wide brimmed hat and sunscreen or zinc on the face for sure

Is the activation period true with a mineral sunscreen, or is that only chemical?

@T.H.O.U. reapplying *doesn't* reset the time to burn, so whether you reapply every 30 minutes, or don't reapply at all and don't sweat it off, you will still burn in the same amount of time.

"A sunscreen’s SPF number is calculated by comparing the time needed for a person to burn unprotected with how long it takes for that person to burn wearing sunscreen. So a person who turns red after 20 minutes of unprotected sun exposure is theoretically protected 15 times longer if they adequately apply SPF 15. Because a lot of sunscreens rub off or don’t stay put, dermatologists advise reapplication every two hours or after swimming or sweating."

http://www.nytimes.com/2009/05/14/fashion/14SKIN.html?pagewanted=all&_r=0

@Mrs. Chipmunk: ok fair. But it does reset your burn time by reapplying. Again if an SPF 15 lets you stay out for a total of 300 minutes and after 120 minutes (2 hours) you assume it's worn off and you re-apply then from that new point forward you have an additional 300 minutes of protection. Again same "time to burn" but the clock resets when you reapply.

I just want to make sure no one is confused and thinks you don't need to reapply because that is one of the biggest mistakes people make with sun care. @Pepper:

@Pepper: where are the pictures of C on vacation?!

@T.H.O.U. i learned in school that it doesn't reset the burn time....

@Mrs. Chipmunk: I did not know that! Interesting!

@T.H.O.U.: I looked it up to verify: http://news.psu.edu/story/141338/2010/06/01/research/probing-question-what-does-spf-rating-sunscreen-mean

@T.H.O.U.: @Mrs. Chipmunk: I'm a scientist and I've actually sat in on a lecture about the science of sunscreen by someone who develops sunscreen for a living.

If applied perfectly (which most people don't do...most people put too little on, and then it gets rubbed or washed off as well...) the SPF does provide a multiplier. If you would burn in 10 min, proper application of the proper quantity of SPF 30 sunscreen would give you 300 minutes to burn. Since it does usually get worn off and often enough isn't used, that SPF 30 might only give you, say, 150 minutes until you burn because it isn't perfect application. Then the reapplication would help give you another 150 minutes. Make sense?

With that said, there's nothing magical about that 149th minute in which you would burn...it's a gradual process to get from tan to burn, unless you've been doing something like swimming where more sunscreen has come off, so keep it in mind, apply more sunscreen than you think, and reapply often!

This is so confusing. How do you reset your time then? By going inside? Then magically you have another 180 minutes or whatever? Do you have to have a certain amount of non-exposure? Wow, I always thought it extended the amount of time... but this does explain why I've gotten burned even when reapplying frequently.

This is new to me, from wikipedia:

Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, research has shown that the best protection is achieved by dividing the SPF number in half and reapplying that many minutes after sun exposure begins. For example, if the SPF is 30, sunscreen should be reapplied once after 15 minutes of exposure. Further reapplication is only necessary after activities such as swimming, sweating, or rubbing/wiping.[60]
More recent research at the University of California, Riverside, indicates that sunscreen must be reapplied within two hours in order to remain effective. Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals from those sunscreen chemicals that were absorbed into the skin.[48] Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a square or 4th root of the advertised value.[61]

I don't know how the time "resets" for let's say, the next day. I would imagine that because the sunscreen itself is absorbing the UV rays, you have to wait out perhaps 7 half lives of the UV rays themselves to be gone.

@mrs. pen @FRONKINZANKINSBRIDE ok, i'll work on one

I agree with @edanda because in her example the max time without a burn is 300 min, so reapplying doesn't give you an extra 150 to make it 450 , but simply makes up for not putting enough on a d/or sweating it out.

Barriers work different than actual sunscreens - sunscreens absorb the uv rays while barriers actually reflect them. Also barriers are probably more likely to get rubbed off. I know I coat my seatbelt and door panels with white paste in the summer from my zinc oxide

@mjane: this is my point. I KNOW I'm able to stay in the sun for much longer without burning by reapplying. I really worry that this could be very easily misrepresented and people think if they aren't swimming or something they don't need to reapply.