How Important is SPF for Sun Protection?

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How Important is SPF for Sun Protection?

When it comes to sunscreen, a higher SPF should protect against more UV rays than a lower one. And it does, but not by much. SPF 15 sunscreen blocks 93% of UVB radiation. SPF 30 blocks around 97%, and SPF 50 blocks 98%. "As you get higher and higher, it's not really a practical difference," American Academy of Dermatology president Dr. David M. Pariser told the New York Times. Here's why: companies calculate SPF by comparing the time it takes a person to burn unprotected with the time it takes for them to burn wearing sunscreen. Therefore, if you burn after 20 minutes with no sunscreen, you should theoretically be able to last for 15 times longer -- a whopping five hours -- with SPF 15. But sunscreen itself doesn't usually last that long. Sweat, friction, and simple quirks of product formulation can make it wear off, which is why dermatologists recommend reapplying every two hours. That means it doesn't really matter whether you get the SPF 30 or the SPF 100, since the formula will probably wear off before the difference in protection becomes important. What is important is applying sunscreen properly: for a full-body application, you should use an ounce of sunscreen, or roughly the volume of a shot glass. And because SPF is only a measure of UVB protection, you should look for a full-spectrum formula that protects againsts both aging-related UVA and sunburn-related UVB rays.

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Key Facts to Know

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    Sunscreens protect skin from UV light, which can damage skin cells and cause sunburn, moles, freckles, and wrinkles. 0:48

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    UV-B light is the primary cause of sunburn. UV-A penetrates more deeply, causing more long-term damage like wrinkles and age spots. Both can cause skin cancer. 1:02

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    SPF 15 protects the skin from 93% of UVB rays. SPF 30 protects it from 97%. 2:38

The Sun Will One Day Consume Mercury And Venus

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The Sun Will One Day Consume Mercury And Venus

Life on Earth came to be billions of years ago, shortly after the planet cooled and liquid water became available. But according to researchers, we only have about one billion years left until life on the surface of Earth is wiped out. Our sun is growing hotter and hotter, and eventually surface life on Earth will be obliterated by the sun's growing radiation. Life beneath the surface, however, has a little more time. The reserves of water deep underground will be able to protect microbial life for billions of years after life on Earth's surface dies off. Meanwhile, in the next 5 billion years, the sun will consume both Mercury and Venus.

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Key Facts to Know

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    Life on Earth appeared shortly after the planet cooled and liquid water became available. 0:03

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    We have less than a billion years to enjoy the surface of Earth before it becomes inhospitable. 0:46

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    Reserves of water deep underground will protect microbial life for billions of years after life on Earth's surface dies off. 2:22

What Would Happen If The Sun Disappeared?

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What Would Happen If The Sun Disappeared?

Early scientists thought that the effects of the sun's disappearance would be instantaneous, and that even if we didn't notice its absence visually, the shift in gravity would be apparent. But we now know that gravity waves travel at the speed of light, which means that the planets would continue to orbit the "gap" where the sun had been for several minutes after its disappearance.

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Key Facts to Know

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    Gravity waves travel at the speed of light. 0:26

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    If the sun disappeared and released Earth from its orbit, Earth would travel at 30 km/s into space. 1:32

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    In the sun's absence, the Earth would take thousands of years to radiate its heat completely off. 2:18