Last weekend, we looked at the regulatory sunscreen drama that’s playing out in the U.S. Congress and at the FDA about what sunscreens should be allowed to be sold in America. Other countries have more modern sunscreens that last longer and prevent more UV light from reaching our skin, whereas the ones sold here tend to be greasier and stickier.
But while that all gets sorted out, we Utahns still need to protect ourselves.
Utah has the highest melanoma rate in the U.S., according to the CDC. Nationally, about 20 people per 100,000 are diagnosed with skin cancer every year; in Utah, that number is about 40 per 100,000. That’s easy to explain: we’re outdoors more often than the average state, and we also have fairer skin on balance than the rest of the states.
So using sunscreen right is more important here than anywhere else. Unfortunately, studies show that people everywhere are pretty terrible at using sunscreen the right way.
You’re familiar with SPF, right? That’s the Sun Protection Factor, which basically measures how much of the sun’s rays get through the sunscreen. If a sunscreen is SPF 30, that means about one in every 30 rays gets through. The experts calculate this by time — let’s say it takes one minute for a section of skin to redden without sunscreen. If it took 30 minutes to redden with sunscreen applied, that sunscreen is SPF 30.
But here’s the catch: in these tests, sunscreen is applied to human skin at two milligrams per square centimeter. In reality, people use half or a quarter of that.
A lot of different studies show that result. My favorite was a study of beachgoers at a nude beach, where they weighed the sunscreen bottles of 42 men, women, and children before and after a full-body sunscreen application. The researchers found that people used 0.5 milligrams per square centimeter, not 2. Another study of people on a one-week vacation to Egypt found men used 0.93 mg/cm², while women used 0.66 mg/cm².
Researchers were curious if application method mattered, and had different classrooms of kids use different sunscreen — if kids used roll-on sunscreen, they got 0.22 mg/cm² on themselves, those with a squeeze bottle used 0.57 mg/cm², and those with a pump bottle used 0.75 mg/cm². No matter what, people aren’t using anywhere near enough sunscreen.
Even if you tell people they’re not using enough sunscreen, they still don’t use enough sunscreen. One study educated people on sunscreen use — “Hey, you need to be using 2 mg/cm². Here’s how much sunscreen that is, here’s how to apply it,” and so on. They raised their application levels to only 1.13 mg/cm².
The problem is that it appears most likely that SPF and application thickness have an exponential relationship. In other words, if you use half as much sunscreen as you should, you only get the square root of the SPF. Using real world numbers: if you have an application thickness of 1 mg/cm², your SPF 30 sunscreen turns into SPF 5 sunscreen. If you have an application thickness of 0.5 mg/cm², your SPF 30 sunscreen turns into SPF 2 sunscreen.
As a result, every study that I was able to find has a curious conclusion: sunscreen use is correlated with increased sunburn. People feel more confident being out in the sun thanks to their sunscreen use, even if it’s spotty or thin.
So what can you do to make sure you’re not falling into that trap? Different dermatologists recommend different tricks. Here were the ones resonating most with me:
• If you do the math on 2 mg/cm², that means the average-sized human should use about 1 fl. oz. of sunscreen every time they apply sunscreen. Increase the amount if you have more skin surface area than the average human. One fluid ounce is a shot glass of sunscreen. Knowing this is also useful if you’re calculating how much sunscreen to bring on a trip.
• How do you make sure you get that much sunscreen everywhere? One fun paper suggested teaching dermatology office visitors about the “rule of nines” — 11 zones of your body that make up about 9% of your total skin each. Those 11 areas: your head, neck, and face; left arm; right arm; upper back; lower back; upper chest; lower stomach; upper left leg; upper right leg; lower left leg and foot; lower right leg and foot.
Each of those should get their own application of “two fingers” of sunscreen — basically, stick out two fingers and squeeze a line of sunscreen from palm to fingertip on each finger.
• Because we know people typically don’t use 2 mg/cm² in a single application, multiple dermatologists recommend just applying sunscreen twice, usually 15 to 30 minutes apart, to get the full dose needed.
• Spray sunscreens can be just as effective as lotion sunscreens, but most people mess up the application. Rubbing the sunscreen in is necessary. Don’t use them if there’s even a light wind, a majority of the aerosol will just blow away. Honestly, perhaps most effective is just spraying the sunscreen into your hand, and rubbing it in to your skin next.
• In part because we have those older, less effective sunscreen filters in the U.S., you’ll need to reapply frequently, at least every two hours. If you’ve been swimming or sweating, every hour is probably more like it.
• Especially here in Utah at our altitude, applying adequate sunscreen is a year-round job. Check the UV index on fall and winter days too, when you’re headed outdoors for a hike or a ski day.
• And frankly, just because you wear sunscreen doesn’t mean you can’t use other sun protection tools. Wear a hat! Find some shade! Take breaks inside! Multiple protections used at once are going to be most effective.
Andy Larsen is a data columnist for The Salt Lake Tribune. You can reach him at alarsen@sltrib.com
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