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How often to apply sunscreen - please help
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Please help me! There are some things about using sunscreens that I just do not understand.
"Reapply sunscreen every two hours." Does this mean after two hours of sun exposure? What if it is applied and then you stay in a dim room and the sunscreen does not get wet, sweated off, or rubbed off for two hours. Does it need to be reapplied again before going outside? Is the answer different if it is a chemical sunscreen or a physical sunscreen?
If I apply sunscreen, then go in the sun for one hour, then go inside for another hour, can I go back in the sun for one more hour before I need to re-apply?
Also, after two hours have passed (with no wetness, sweating, or rubbing off of sunscreen), do you now have no UV protection at all, or is there still some SPF, maybe a reduced SPF, that continues to give you protection?
I understand that chemical sunscreens break down as they absorb the UV light, which necessitates re-applying the sunscreen. What about zinc oxide or titanium dioxide sunscreens. If they do not get wet, sweaty, or rubbed off, why don't they protect for longer than two hours?
I need to know because I have not bothered putting sunscreen on my 8 year old before she leaves in the pre-dawn hours for school, figuring that by the time she is outside getting UV exposure, more than two hours later, she won't be getting any protection anyway. But I would apply it if I thought it would give her some protection.
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I would guess she would still be getting a fair amount of protection. But you're not *guaranteed* full protection unless you reapply. I would guess the amount of reduction in protection is quite dependent on friction, sweating, etc. I'm bad about reapplying at the beach, but if I use water resistant sunscreens, I never burn despite not reapplying. Maybe I'm getting more age damage than I need to, but I don't burn, so I must still have some protection (that's even after swimming).
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I found this at the American Melanoma Foundation's website but there iis nothing about the need to reapply it if you stay dry:
"Sunscreens should be applied in the morning and reapplied after swimming or perspiring heavily. Remember, waterproof sunscreen begins losing effectiveness after 80 minutes in the water, so reapply sunscreen before this time, especially if you have towel-dried for maximum protection."
Here's the link to the full article:
http://www.melanomafoundation.org/prevention/facts.htm
Now I'm curious! Has anyone else heard you need to reapply it, even if you stay dry? -
Right, Karen, I think the recommendation is definitely to reapply--my understanding is that's even if you're not swimming, but right away if you have been swimming. But my guess is that even if the protection is sub-optimal or even inadequate without reapplying, you are probably still getting some residual...at least some residual protection hours later (say to the daughter of the OP) is better than if you never applied at all, if that makes any sense. I think the publicity about this is so that people aren't lulled into a false belief that "just because I put sunscreen on once, I'm getting full protection all day." As long as the public is informed about the risks of not reapplying, they can decide based on their skin type, activities and amount of time spent outdoors how much risk they're comfortable taking. But getting back to your question, I'm not positive as to the exact guidelines on reapplication if you stay dry. Might check the fine print on a new tube of sunscreen and see if there's a blurb on it about that.
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Two follow-ups:
1) disclaimer--when I said I didn't burn despite not reapplying, I was in no way recommending anyone else try it at home. It is safest to reapply. And I'm not one to spend all day at the beach, otherwise I would certainly burn.
2) Apparently, the current recommendation of the american academy of dermatology is to reapply every 2 hours no matter what. I am sure I will be sorely punished with wrinkles or (god forbid) a skin cancer, but I can't see myself becoming quite that thorough. We'll see--maybe I can discipline myself. Maybe I'll get an ultra-modest bloomer bathing suit. Although the truth is I'd guess I don't even spend much more than two hours at the beach these days. Anyway, see link...
http://www.aad.org/public/sun/smart.html -
When my kids were little, I had stickers that I'd put on their skin and then I'd apply the sunscreen over them. When the sunscreen had worn off, this stickers would turn red and you knew it was time to reapply. I think I got them at Right Start, which is no longer in business. I know that they're intended for kids but there's no reason an adult couldn't use them. You could use them just a few times until you had a better idea of how often you need to reapply.
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Thank you everyone for your responses. PurpleRules, I really have to get some of those stickers.
I also did a search on this topic and found this article on Makeup Alley. In the section headed "How often do I need to to re-apply sunscreen?" the writer quotes a dermatologist as saying that the AAD's recommendations about how often to reapply refer to how much time you have spent in the sun. I.e., reapply after two hours in the sun. I take this to mean that if you are spending four hours going in and out of doors, with no more than two hours outdoors, you would not have to reapply.
The article also says that photostable sunscreens may protect for longer periods of time in the sun, provided you stay dry.
This is great news for me, since I now can re-apply less often. I use Vanicream SPF 30. If I spend a little less on sunscreen, I'll have more money for something frivolous.
This link is to the article:
http://makeupalley.com/user/notepad/sunscreenFAQ -
If you use 30 SPF, you will be protected for (15 minutes x 30 = 450 minutes) around 7 1/2 hours. If you use 40 SPF, the protection will last for about 10 hours. But that 10 hours applies only if you aren't swimming or perspiring. If you are active or if you get wet, you need to reapply the sunscreen after 60-90 minutes. Keep in mind that everyday liberal application, applied 20 minutes before you step outside is the key element of getting the best protection possible. Look for sunscreen products containing UVA protecting ingredients such as avobenzone, titanium dioxide, zinc oxide, or Mexoryl SX. You can read more information about what types of UV rays are there and why it is important to apply sunscreen protecting both UVA & UVB rays from http://www.thevanya.com/blog/featured/what-are-uv-light-rays-protection
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The SPF indicates how much extra protection the sunscreen provides to an individual, based on their sensitivity to the sun, so it varies per person. If your unprotected skin burns after 20 minutes of sun exposure, an SPF of 15 would protect you 20 minutes x 15; but if you burn in 5 minutes, obviously the same SPF would provide protection for a shorter period of time. For more, please read: http://www.skincancer.org/sunscreens-explained.html
This doesn't really answer the OP, but I wanted to add some clarification on what the SPF on a bottle or tube of sunscreen signifies.
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