While I was reading about higher SPF levels in sunscreen, I had a disconnect when I got to the part that describes the strength of a particular SPF level. You say that SPF indicates how long the sunscreen will last; however, you then go on to say that one should reapply sunscreen every hour or two.
Assuming I use a SPF 15 sunscreen, this means that I will be protected for 150 minutes, clearly longer than 1 or 2 hours. And if I were to use SPF 100, that's 1000 minutes, more than 16 hours! Even if conditions weren't perfect, that should protect me for the whole day! Why would I then need to reapply every hour or two?
This is just part of a wonderful email that I got from a reader named Vincent. He brings up such a good point, and my guess is, so many others might have a disconnect with our recommendations of applying sunscreen every 1 1/2 to 2 hours that I would share what I wrote back to Vincent.
I am so glad that you are researching sunscreen. You're absolutely right, there are so many opinions and so much information to go through and then you have to decide what you think is best.
Have you heard about the new FDA mandated sunscreen label changes that are taking place the summer of 2012 and 2013? Here's an article explaining the changes sunscreen companies will be making. This will help make sunscreen protection more understandable.
There are too many factors that can involve a sunscreen's ability to be effective as long as they should be. People don't use enough, people sweat, people are in the pools, kids are in the sprinklers, etc. Then you add on top of that the sunscreen labels that are telling you they are waterproof. (They're not.) People get a false sense of security.
I know I am in the conservative side when it comes to sunscreen application recommendations, but I'm also a redhead with very fair skin and my skin cancer risk is high. And I'm a mom who has a goal that her children never get sunburned. So being conservative is something I'll readily admit to and likely always will be.
If you look at a bottle of sunscreen, no matter the SPF level, it will say something along the lines that it retains good coverage when in the water for up to 80 minutes. Less than 1 1/2 hours. Most people sweat while outside in the summer. Likely not profusely, but sweating none-the-less. When the FDA changes come to sunscreen bottles, they will need to be tested to make sure they do provide coverage while the body is wet for 80 minutes. If they don't, they'll have to pass the 40 minute test. 40 minutes! Less than an hour. Even if it's SPF 50!
So many people go to water parks with good intentions, buying the "waterproof" sunscreen with a high SPF and put it on a couple times during the day. And so many of them wind up with a sunburn, confused because they thought they were doing things correctly. The label says so, right? But when they see the 80 minutes on the label, they're surprised. Imagine what people will think when they see 40 minutes on the label.
So, call me a little sunscreen obsessed (I am.) and maybe I spend too much money on sunscreen, but I have read time and time again by different Dermatologists that people just don't use enough sunscreen. People look at labels and think they're truthful. (Have you seen the labels that say "All day protection"? Labels will not be allowed to have that on their labels come next summer.)
And lastly, yes, I did put the calculations out there, but please don't forget that right at this moment, until the summer of 2012 and 2013, there is no indicator of how much UVA protection a "broad spectrum" sunscreen has. It could have the smallest amount of UVA protection and still be called "broad spectrum". UVA rays are the rays responsible for cancer and aging signs. So, while a sunscreen can give good protection against sunburns (UVB rays) but just a little protection against UVA rays, applying more frequently will never be a bad thing. Come 2012 and 2013, there will be tests to make sure the "broad spectrum" brands really do provide good coverage against both UVA and UVB.
So, that's why we say it's a good idea to apply every 1 1/2 to 2 hours, even if the calculations don't add up.