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  • I love the sun, don’t you?

  • It makes the plants grow.

  • It keeps me warm.

  • Helps me make Vitamin D. And - incessantly bombards me with dangerous UV radiation.

  • That’s right.

  • The sun is both our friend, and our enemy.

  • Our big, burning frenemy.

  • Don’t go out there without protection.

  • Sunglasses.

  • Long sleeves, big hat - and sunscreen.

  • You know the Sun makes visible light - it lights up everything we see!

  • Even the moon.

  • But today, were talking about the light we CAN’T see.

  • There’s infrared - that makes up about half of the Sun’s energy that hits the earth.

  • Although it’s invisible, infrared radiation keeps us nice and cozy.

  • But that’s not what’s going to give you a sunburn or make you have wrinkles, or cause

  • skin cancer.

  • I’m talking about UV.

  • Ultraviolet Radiation.

  • About 8 percent of the Sun’s radiation is in this part of the spectrum.

  • UV light has a shorter wavelength than visible light.

  • MOST of the Sun’s radiation gets filtered out by our atmosphere, thank goodness.

  • This is one of the challenges of space travel, by the way - you want to be an astronaut,

  • youre going to have to protect yourself against UV radiation - no more Earth’s cushy

  • atmosphere protecting you.

  • Our ozone layer catches a good portion of UV.

  • But some of it still reaches us down here on the ground.

  • How much UV are we exposed to?

  • That depends.

  • Where are you on Earth?

  • Are you on the top of a mountain?

  • How far are you from the equator?

  • What season is it?

  • What time of day?

  • The peak hours for UV radiation are 10AM to 4PM.

  • Is it cloudy?

  • Around 20% of UV radiation can be blocked on an overcast day.

  • Is there anything reflective near you?

  • Water/snow/sand?

  • Those rays are going to reflect right back at you.

  • Double whammy.

  • All these factors will affect how much UV radiation reaches you.

  • Do you know your UVI?

  • The Ultraviolet Index is a rating scale, with numbers from 1 to 11.

  • The higher the UVI number, the more intense the UV rays you will be exposed to.Thedaily

  • UVIforecasts the amount of UV reaching your area at noon - when the sun typically

  • reaches its highest point in the sky.

  • If you want to get into specifics, there are websites you can visit and apps you can download

  • to let you know what is your UV exposure on any given day, at your specific location.

  • For example, in the United States, The Environmental Protection Agency (EPA) offers UVI forecasts

  • by ZIP code on their UV Index page.You can even buy a little meter so you can make the

  • measurements yourself.

  • Well include links in the description below.

  • This is all to say - you need to take steps to protect yourself from UV radiation.

  • You can wear protective clothing - like this shirt I’m wearing was advertised as sun

  • protection.

  • The tighter the weave, the more protection your clothes will offer you.

  • Now keep in mind, the protection generally goes down when it gets wet.

  • Still, it’s not like I go around bundled up all the time.

  • I don’t know about you, but when it’s burning hot out, and I start shedding layers,

  • I want to slap on some sunscreen.

  • Let’s talk SPF.

  • The effectiveness of sunscreen is measured in terms of FACTORS.

  • That’s what SPF stands for: sun protection FACTOR.

  • This depends on YOU.

  • Your baseline determines how well the sunscreen will work for you, personally.

  • It’s not going to work exactly the same for you and all your friends, unless you just

  • randomly happen to have exactly the same amount of sun tolerance.

  • So let’s say you, PERSONALLY, can stay out in the sun for 15 minutes before you start

  • burning.

  • And you put on some sunscreen that is SPF 20.

  • Think of multiplying your personal tolerance by a FACTOR of 20.

  • 15 minutes x 20 = 300 minutes, or 5 hours.

  • So this kind of sunscreen should, theoretically, protect you for up to 5 hours before you start

  • burning.

  • Hey, great, youre thinking.

  • That means I can put on sunscreen and go out for 5 hours without thinking about it!

  • NO, no good, stop it, no wonder youre a lobster!

  • Sunscreens aren’t magic.

  • They wear off, they rub off, they sweat off.

  • Most dermatologists recommend reapplying sunscreen every 2 hours.

  • But you should re-apply even sooner if you noticed you rubbed off on a towel, or washed

  • your hands, or whatever.

  • And just how much did you put on?

  • Most people don’t put on nearly enough sunscreen.

  • In fact, one study showed that it was best if you told people to put sunscreen on TWICE

  • - because then, they *might* put on enough sunscreen.

  • The general recommendation is 1 oz - about a shot glass full.

  • That’s a LOT of sunscreen.

  • Have you been putting on enough?

  • Don’t forget your ears, and the tops of your feet.

  • A lot of people skip those spots.

  • This is what you should be aiming for.

  • This man put sunscreen on one half of his face.

  • Then a photo was taken with UV light, so you can see just how much of the UV is absorbed

  • in the areas where he put on sunscreen.

  • Everywhere UV is absorbed, his face is dark.

  • Nice work, pal.

  • Now let’s take a closer look at the enemy.

  • UV can be broken down into 3 subclasses of radiation - UVA, UVB, and UVC.

  • UVC has the shortest wavelength - 100-290 nm.

  • It’s completely caught by our ozone layer.

  • So, let’s cross that off our list of things to worry about today.

  • UVB is the next longest wavelength - 290 to 320 nm.

  • UVB is partly blocked by the ozone layer.

  • Also, if youre working in an office or driving in your car, no worries.

  • UVB can’t travel through glass.

  • This is the UV radiation that gives us a sunburn.

  • Ouch.

  • UVA is the longest wavelength - 320 to 400 nm.

  • This kind of UV radiation penetrates the ozone layer, glass, and goes into the deeper layers

  • of our skin.

  • This is the kind of UV radiation that causes wrinkling and those unpredictable age spots.

  • According to the American Cancer Society, most skin cancers are a direct result of exposure

  • to the UV rays in sunlight.

  • Skin cancer has also been linked to exposure to artificial sources of UV rays, like tanning

  • beds.

  • So - other than the obvious - avoiding the sun and artificial UV, how do you protect

  • yourself?

  • Look for a sunscreen that saysbroad spectrumon it - and it should spell out, in the fine

  • print, that it protects against UVA *AND* UVB radiation.

  • You have a choice when it comes to sunscreens.

  • Physical, or chemical?

  • Physical sunscreens are a literal PHYSICAL barrier to UV radiation.

  • These are inorganic compounds, like zinc oxide or titanium dioxide.

  • In the early days of sunscreen, these looked a lot like white paint.

  • Now with more advanced manufacturing, we can make nanoparticles of these materials, so

  • they practically look transparent.

  • But those particles are still in there, physically reflecting and scattering the UV rays.

  • There’s a wider variety of CHEMICAL sunscreens to choose from.

  • These are organic compounds that actually ABSORB UV rays and TRANSFORM the energy of

  • the radiation into a different form.

  • It’s released as heat - and so it can no longer harm you.

  • Some common chemical sunscreens include Para Amino Benzoic Acid (PABA); oxybenzone, avobenzone,

  • octyl salicylate - many sunscreens contain a mixture of ingredients, with each chemical

  • playing a different role.

  • Some are better at dealing with UVA, some handle UVB.

  • Most UV protection works better when it works in concert.

  • One concern is that using some chemical sunscreens gives rise to problems in the environment.

  • For example, several sunscreen ingredients were shown to kill or bleach coral, even at

  • extremely low concentrations, including oxybenzone, butylparaben, and octyl methoxycinnamate.

  • So do your research - many sunscreen bottles let you know if they are reef safe.

  • Now go out there and enjoy some time with our dangerous friend!

  • But let’s be safe out there!

  • Where are my sunglasses?

  • Do you love watching high quality educational videos?

  • If you find our content helpful, please consider becoming our Patron on Patreon.

  • Your support means we can keep making videos for everyone to enjoy.

  • Thanks from all of us at Socratica.

  • Heads up!

I love the sun, don’t you?

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SPFの科学 - 日焼け止めはいかにしてあなたを安全に保つか! (The Science of SPF - How Sunscreen Keeps you Safe!)

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    林宜悉 に公開 2021 年 01 月 14 日
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