Math is a beach, sometimes
Published 12:56 am Wednesday, May 20, 2009
It’s bare skin time. Yep, time to pull off winter clothes and jump into shorts and tank tops and swimsuits. At the beach, by the pool or in the back yard, bare is better when it’s hot weather.
Of course too much of a good thing is not necessarily a good thing, and that includes soaking up the rays. So being a responsible person, I decided to purchase sunscreen and discovered a bunch of new numbers on the products.
Stamped in large print were SPFs (Sun Protection Factor) of 50, 75, even 85. I was confused; I mean what happened to good old SPF 30? Wasn’t that enough to stop even the palest among us from burning?
Turns out there is a controversy raging over the whole SPF thing, and apparently it takes math to make sense of it all.
According to a story in the New York Times, sunscreen’s SPF measures how much the product shields the sun’s shorter-wave ultraviolet B rays, known as UVB radiation, which can cause sunburn. Well, that’s a mouthful isn’t it?
In the good old days, the SPF topped out at 30. Now companies work overtime to develop higher and higher SPF’s. Do they offer better protection? Not necessarily.
This is where it gets confusing because you start talking percentages and square roots and other math stuff, which I have admitted on more than one occasion, gives me a headache.
To begin with, I learned you calculate a sunscreen’s SPF number by comparing the time needed for a person to burn unprotected with how long it takes for that person to burn wearing sunscreen. Here comes the math — so people who turn red after 20 minutes of unprotected sun exposure are, theoretically, protected 15 times longer if they adequately apply SPF 15, according to that New York Times story again.
In order to get the full SPF protection, you must, I learned, use the correct amount on your body, which the writer said equals a full shot glass or about an ounce. If you don’t use the right amount, the math gets so complicated they brought in an expert to explain it.
“It turns out that if you apply half the amount, you get the protection of only the square root of the SPF,” said Dr. Darrell S. Rigel, a clinical professor of dermatology at New York University, who has done efficacy testing for Johnson & Johnson and the Procter & Gamble Company. So applying a half-ounce of SPF 70 will not give you the protection of SPF 35, but 8.4, Dr. Rigel said.
Dear goodness, I only want to keep myself from frying like a chicken, and now I’ve got to figure out if I’ve used exactly an ounce and if I didn’t, then I calculate the square root of something. How do you figure out when an ounce has come out of a spray can because my sunscreen sprays?
I also need to block different kinds of rays and even a 100 SPF might not do that job. I read this:
“…dermatologists now advise using sunscreens with an SPF of at least 15 and UVA-fighting ingredients like an avobenzone that doesn’t degrade in light or Mexoryl SX.
The difference in UVB protection between an SPF 100 and SPF 50 is marginal. Far from offering double the blockage, SPF 100 blocks 99 percent of UVB rays, while SPF 50 blocks 98 percent. (SPF 30, that old-timer, holds its own, deflecting 96.7 percent).”
I do not know what percentage the sunscreen I bought offers, but I’ll be darn if I’m taking a calculator to the beach to figure it out. Nope, I’m thinking I’ll get myself a big old straw hat, a long sleeved shirt and a shot glass full of something to help me forget the danger of stepping out into the sun.
My SPF might not be adequate, but I’ll be happy while I burn.