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 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 generally, 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,
UVB是较强的光 能导致晒伤 引发特定皮肤癌
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主要晒黑皮肤 引发使身体释放吸光的化学物质 黑色素
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.
UVA能导致皮肤老化 白内障 癌症
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.
Fine 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,
暴露在能使皮肤老化 伤害眼睛 免疫抑制 导致癌症的UVA下
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 out 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!