Friday, February 12, 2010

Suncreen and SPF

We should all know by know that sunscreen is vital when it comes to preventing photo-aging (which is aging caused by the sun’s rays), and keeping our skin looking younger and better for longer. I think some of us also remember the bit of controversy surrounding independent makeup companies claiming an SPF rating on their products, when SPF ratings can only be given obtained by extensive FDA testing. In this post, I will cover what UV rays do to your skin, how the FDA tests for SPF, what the FDA SPF recommendations are, and what those recommendations are based off of.

Let’s talk about sun, baby.
We’ve all been told that UV rays are bad for us, but what kinds of UV rays are out there, and what do they do? There are two types of UV rays that we need to be concerned with when it comes to our skin: UVA, and UVB. They’re both plenty damaging to our skin, but we tend to think of UVB rays as being worse for us, because those are the rays that cause our skin to burn. However, these rays are short-wave, and do not penetrate very far down into the skin’s surface. And while each sunburn your receive doubles your chances of getting skin cancer, what we really need to worry about are UVA rays, which are long-wave, and penetrate deep into the skin. Why do we need to worry? UVA rays account for 95% of the sun’s radiation on the earth’s surface, so those most damaging rays are also the ones that we are exposed to most frequently.

Burnin’ up.
So, have you ever wondered exactly how it is that the FDA tests for SPF? Well that’s what I’m here for, to act as your font of knowledge, quenching your thirst for information. Sorry for the awful metaphor, sometimes I can’t help myself. Anyhow. The reason SPF testing is so expensive, and so time consuming, is that the FDA must perform it, and it isn’t a test of chemical composition of the product, it is tested on people. First, the FDA will gather a whole lot (that’s a scientific measure, y’all) of tests subject of varying ages, skin types, and skin tones. Then, one by one, they will test the product to determine its SPF rating. They divide a subject’s back in half with some sort of divider (my professor was not clear on what was used to divide), and on each side of the divider is a Xenon lamp. The way that they test SPF is by putting an FDA regulation control cream with an SPF of 2 on one side of the person’s back, and the test product on the other side, and turn on the lamps. When a burn becomes visible (presumably on the control side), they turn the lamp for that side off, and wait for a burn to become visible on the test product side, all the while, timing the procedure. Here he mentioned something about dividing the time it took the test side to burn by the time it took the control side to burn to determine the SPF, but the Wikipedia page on sunscreen provides a much more complex, and confusing equation. Either way, that’s how it’s done, and that’s why it’s so difficult, as well as expensive to determine SPF. So, word to the wise: if you see a small, independent makeup company who claims that their products have an SPF of “X”, you might want to reconsider before buying.

So, like, how much sunscreen should I wear, anyway?
Well, I’m glad you asked. You see, the FDA has a nifty chart for recommendations on how much sunscreen one should use for their skin type. I stole this one from my professor’s notes:

Now, it needs to be noted that these recommendations are based on you using 2 mg of sunscreen per cm² of skin, and re-applying every two hours. Now that might not make a lot of sense, but if you were using that much sunscreen, it would be a visible layer on your skin, and you know that you probably don't re-apply every two hours, especially if you're having fun at the beach or pool. Since we don't use that much and don't tend to re-apply frequently, my professor recommended doubling the FDA's recommended SPF, and going with that, so that you can achieve the maximum amount of protection possible.

More isn’t always that much better.
What SPF means is that the sunscreen will protect x amount times more than your skin would protect you with no sunscreen. More specifically, SPF 30 will protect you from 98.5% of the sun’s rays. However, since SPF suns on a bit of an exponential curve, meaning that the amount of harmful rays you’re exposed to decreases rapidly with sunscreen, but slows down a great deal as you reach further. So despite SPF 60 sunscreen being twice as powerful as SPF 30, it only blocks 1% more rays, at 99.5%. So really, there’s probably not a reason most people would need SPF 60 sunscreen, unless they are so intensely sensitive to the sun that they need that extra 1% of protection. However, since most of us don’t need it, it’s probably not a good idea to pay the premium that high SPF sunscreens tend to run, and just reach for the SPF 30 instead.

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