Beauty Logic: Understanding SPF Monday 02 July, 2012
I have a bone to pick with my brain: When it comes to retaining information that I just read, it likes to hide bits and pieces of it. To say that I have “recesses” in my noggin is an understatement; there’s some black-hole shit going on in there, and I don’t like it one bit. […]
I have a bone to pick with my brain: When it comes to retaining information that I just read, it likes to hide bits and pieces of it. To say that I have “recesses” in my noggin is an understatement; there’s some black-hole shit going on in there, and I don’t like it one bit.
This scenario happens all the time: Karie listens to some amazing news story on NPR/reads some enthralling article in Elle/watches some funny show on television. Karie wants to retell said story/article/show to a friend or colleague or acquaintance (though she knows better than to attempt this “feat” with the last one in this series). She starts to tell the story, and then realizes she only remembers a fraction of it—and mostly not the important parts. Such was the case this past weekend when she (or, rather, I) launched into a “this is what SPF means” fact-skewering talk to her husband while they sat poolside.
See, over the years, I’ve learned about SPF. And, lord knows I understand it’s basic principles. But, when I tried to explain SPF to my husband, it came out like gobblegook.
Me: “SPF goes like this: If it takes you 15 minutes to burn without SPF, an SPF 4 would provide you with 60 minutes of protection. So, 4 times 15 equals 60. The same principle applies to SPF 40; you then take 40 and multiply it by 15, and you get 600 minutes of protection.”
Him: “Then why would you ever wear SPF 4? You just end up reapplying it more. I would never wear SPF 4 then. Seems like a waste.”
Me: “Hmmm. Good point. I’m not sure.”
So, back to the drawing board I had to go; I’d just read my SPF multiplication factoid, and I was pretty certain I was right about it. But, he had a point: Why wear a lower SPF if it simply means you have to continuously reapply? And thus, the search for answers began—because I couldn’t remember half of what I read, though I knew I’d read the answers…somewhere. Here we go again…
1. SPF stands for Sun Protection Factor, and the assigned number (i.e. SPF 10) helps you determine how long you can stay in the sun before burning to a crisp. As I mentioned above, it’s a multiplication factor (ha, I was right!). If it takes you 15 minutes to start burning, an SPF 10 would help you stave off those UVB rays 10 times as long. So, 15 x 10 = 150 minutes before you burn.
2. Notice how I only mentioned UVB rays. Yep, SPF only measures protection against UVB rays, which are the ones that create sunburns. UVA rays, on the other hand, are the culprits behind premature aging—but they are not measured by SPF.
3. Because SPF is a multiplication factor, you can’t just add SPFs together and cross your fingers, hoping for the best. What I mean to say is: You can’t apply an SPF 40, and then layer it with an SPF 15, and think you’re getting an SPF 55. Due to the way that sunscreens’ active ingredients work, layering them doesn’t increase their efficacy.
4. Now, multiplication seems easy as pie, right? So why do you still burn sometimes when you apply your sunscreen? Many professionals want you to know: You may feel a false sense of security with SPF because you tend not to apply enough sunscreen. So, even though you did your handy math (SPF 40 x 15 minutes means I can bake for 600 minutes without chance of burn, right?), you may end up burning IF you didn’t apply the right amount of sunscreen. Most people apply HALF the amount they are supposed to. (Find out how much you should apply here.)
5. So…the real question, the one posed by my husband, is: Why doesn’t everyone just wear SPF 40? Or, can SPF 4, reapplied over and over and over again, work as well as SPF 40? Well, turns out I didn’t know the answer off the top of my head, but I do now: SPF also indicates the level of UVB absorption, which doesn’t increase exponentially. For example, an SPF 15 absorbs 93.3% of UVB rays, while an SPF 30 absorbs 96.7%. In other words, though SPF 30 appears to be twice that of SPF 15, it isn’t.
6. Part of the new FDA regulations on sunscreen labeling has to do with UVB absorption. The thought process goes like this: Sunscreens with an SPF 30 or higher should just be labeled “30-plus” because the average of UVB absorbed over SPF 30 only increases slightly with each SPF increment. Why even impose this SPF cap? Because people believe an SPF 50 is a much higher level of protection over SPF 30, when in fact, it’s not. (The difference in UVB absorption: 96.7% vs 98%.)
So, to sum up: The reason why you’d use an SPF 4 is because it’s UVB absorption rate is lower, allowing you to tan slightly more than an SPF 40—no matter how many times you reapply the SPF 4.
Glad I could figure this one out. Now, I’d like to be poolside again, debating sunscreen issues. Sadly, I’ll just be in my dungeon, at my office desk, typing away…
What sun-safe practices do you use?