[INTRO]

Everyone with sunburn-prone skin, like myself, has their own little tricks to steer clear of the sun’s ultraviolet wrath.

It is, after all, a deadly laser! But some of the things people do to keep themselves from getting burned aren’t nearly as effective as you might think.

And long-term, some can be more dangerous than just wearing enough sunscreen in the first place. Like for example wearing clothes. Tan lines might give you the impression that all clothes are perfect sun blockers.

But even though some clothes are better than the best sunscreens, others don’t do very much at all. Sunburn and tans are both caused by the sun’s ultraviolet light interacting with and damaging your skin in different ways. And some materials are better at blocking UV than others.

So jeans, for example, are pretty much perfect for sun protection. Jeans block about 99.94% of UV, which means you’d have to wear an SPF 1700 broad-spectrum sunscreen to do any better. Since they're made of thick, tightly-woven fabric, jeans happen to be especially good at blocking UV.

And in general, most fabrics made with shiny, synthetic, or tightly-woven fibers provide lots of UV protection. Polyesters, plastics, and nylons all generally block at least 98% of UV light, which makes them at least as good as SPF 50 sunscreen. But then there are things like white cotton shirts, which don’t block more than about 75% of UV.

So they’re no better than about SPF 5. Which means that if you wear sunscreen on any exposed skin — even if it’s just SPF 10! — the skin under a white cotton t-shirt can burn before the rest of you does. So you can still get sunburned through some clothes.

Another surprising thing you can get sun damage through is glass. Scientists split the UV that hits Earth’s surface into two categories: UVA and UVB. Regular glass blocks UVB, the more energetic kind of light that mainly causes sunburns and certain kinds of skin cancer.

So you’re mostly safe from sunburns behind a window. But that’s about where the good news ends, because UVA, the less energetic type of UV, can pass through glass. UVA mainly causes tans, where your body releases a light-absorbing chemical called melanin to stop the UVA from doing too much damage to your skin cells.

The melanin is what darkens your skin. But the cell damage from UVA can also lead to skin aging, cataracts, and cancer. So even though you won’t get burned through glass, you’re still at risk for more of all those problems on long road trips.

Glass can be treated so that it also blocks UVA. But in a car, the windshield is often the only glass given the full UVA treatment. Tinted windows can also help a bit, but they’re not always as helpful as just wearing regular sunscreen if you’re going for a long drive.

But you know what’s even less helpful than untreated glass? Getting a base tan. Tanning salons make tons of money convincing customers that tanning before going out in the sun will keep their skin safer for longer without any additional risks.

There is some truth to this, because tanned skin will take longer to burn. But it’s completely untrue that tans don’t carry their own risks. Since darker skin has more melanin, it’ll absorb more UV light and help protect against some of the damage that would eventually cause a sunburn.

But you can still get burned with a tan; it just happens more slowly. And the cost of that tiny increase in sun protection was exposure to lots of skin-aging, eye-damaging, immune-suppressing, cancer-causing UVA while your body was building up melanin. Which is why indoor tanning in the United States is linked to about four hundred thousand cancer cases annually.

And that just doesn’t seem worth it. Maybe an industry whose time has come... Thanks for watching this episode of SciShow.

If it made you want to cover up or just have a good guide for which levels of SPF you should be using, check our SciShow beach towel at DFTBA.com. It has a handy infographic about sunscreen strength and some great little facts about pools and urine. Because, you know, science is sexy!

[OUTRO]