It stands for sun protection factor, and based on that name, it seems like it should tell you how well you'll be protected from the sun.

它代表日光保護係數，根據這個名稱，看起來它似乎會告訴你，在太陽底下你能夠受到多大程度的保護。

Except… that's not totally true.

只是...... 這不完全正確。

Because while SPF might sound like a perfect, rational scientific unit, there are a lot of flaws in the way it's named and the way it's tested.

因為，儘管 SPF 聽起來是個完美、合理的科學單位，它的命名及測試方式中存在著很多瑕疵。

So if you want to be as protected from the sun as possible, you're going to have to know a lot more than that one number.

所以如果你想盡可能地防曬，你需要知道許多除了那個數字以外的東西。

First, as a disclaimer, it's worth noting that countries approach sunscreen regulations differently.

首先作為聲明，要注意，各國對於防曬乳法規有不同的對應方式。

This episode is a good general overview, but keep in mind that things might be different where you live.

這集是一個好的總覽，但是要記得情況會根據你住的地方而有所不同。

Okay, that being said, onward.

好的，話雖如此，繼續。

Essentially, SPF measures how much radiation is blocked from reaching your skin.

基本上，SPF 測量有多少輻射被阻擋到達你的皮膚。

So if it's SPF 30, it will protect you against thirty times more exposure than if you didn't wear sunscreen.

所以如果是 SPF 30，比起你沒有擦防曬乳的時候，它可以減少 30 倍的曝曬。

That translates to roughly 97% protection, and it explains why anything higher than SPF 30 isn't that much more effective.

這大約等於百分之 97 的保護，也解釋了為什麼任何 SPF 30 以上的東西並不會更加有效。

SPF 50, for example, blocks fifty times the radiation, or 98% of it.

比方說 SPF 50，阻擋 50 倍的輻射，或是百分之 98。

Which isn't that different.

並沒有多大的不同。

Still, regardless of what that number says, SPF only tells you how protected you'll be from a specific type of radiation.

不論這個數字代表什麼，SPF 只是告訴你，你會免於受到哪一種特定輻射的傷害。

The rating you see on sunscreen bottles is only required to show protection against UVB rays, the type of radiation that causes sunburns and leads to skin cancer.

你在防曬乳瓶子上看到的分級只需要標示針對 UVB 射線的保護，這種輻射會造成曬傷並導致皮膚癌。

It doesn't have to show protection against UVA radiation, which causes wrinkles, premature skin aging, and again, skin cancer.

它不需要標示針對 UVA 輻射的保護，這種輻射會造成皺紋、皮膚過早老化，以及皮膚癌。

So even if you're using SPF one thousand, that doesn't mean you're protected against UVA.

所以就算你使用 SPF 一千，這並不代表你就可以防止 UVA。

If you want to avoid both kinds of rays, you'll need to look for broad-spectrum sunscreen.

如果你想要避免這兩種輻射，你需要尋找 broad-spectrum 防曬乳。

Another thing worth knowing about SPF is that the way it's tested isn't bulletproof.

另外一件關於 SPF 應該要知道的事情是，它受測試的方法並不完善。

To figure out how much UVB something blocks, you'd think scientists would use some sort of skin-like compound in a Petri dish.

要釐清一個東西可以阻擋多少 UVB，你可能會以為科學家會用某種類似皮膚的化合物放進培養皿。

Like, just shine some light on this stuff, and see how much radiation gets through.

像是，照點光在那些東西上面，看看有多少輻射透過去。

But while that is how they test broad-spectrum sunscreen, it isn't how they test SPF.

儘管這是他們測試 broad-spectrum 防曬乳的方式，卻不是測試 SPF 的方式。

To get an SPF rating, researchers use volunteers.

要得到 SPF 的分級，研究人員會找來自願者。

First, they shine a UV lamp on one spot on participants' bare backs to get a baseline for their tendency to burn.

首先，他們將 UV 燈照射在受試者裸背上的一點以得到他們易曬傷程度的一個基準。

Then, a lab tech applies a gob of sunscreen to a different spot and allows it to dry.

接著，一位實驗室人員將一抹防曬乳塗在不同的點上，等它風乾。

Finally, the tech turns the UV light back on, and sees how much longer the participants last before turning red again.

最後，測試人員再將 UV 燈打開，並觀察受試者的皮膚再經過多久才會變紅。

If they burned in four minutes unprotected, but 60 minutes with sunscreen, that earns an SPF fifteen rating.

如果他們在沒有保護的情況下在 4 分鐘內曬傷，而在有擦防乳的時候，在 60 分鐘內曬傷，這樣就可以得到 SPF 15 的等級。

And if this process seems sketchy and full of issues…

如果這個過程看起來很可疑而且充滿問題......

Yes.

沒錯。

Yes, it does.

確實如此。

For one, people turn red at different amounts of exposure.

首先，人們的肌膚會在不同的曝曬量下變紅。

So if you used a bunch of pale people in one study and a bunch of people with darker skin in another, you'd get totally different results.

所以如果你在一個研究中採用一群淡膚色的人，在另一個研究中採用一群膚色較深的人，你會得到完全不同的結果。

And then there's the amount of sunscreen used in these tests.

接著還有在測試中所使用的防曬乳量。

While there's tons of variability between testers, protocol calls for no less than two milligrams of sunscreen per square centimeter of skin.

儘管受試者之間有超多變異性，規定要求每一平方公分的肌膚不得少於兩毫克的防曬乳。

And that's significantly more than people tend to use in real life.

而這比人們通常在現實生活中所使用的多出非常多。

In one study, it was more than twice the amount.

在其中一個實驗中，它使用了兩倍以上的量。

Ultimately, these tests just aren't representative of what happens in the real world.

最終，這些測試根本無法代表現實生活中所發生的狀況。

They don't take into account things like skin color, or how much sunscreen people actually use.

他們不將膚色或是人們實際上使用了多少防曬乳納入考量。

So when you're buying this stuff, it's probably worth keeping those things in mind.

所以當你在買這個東西時，最好將這些事記在心裡。

For example, maybe this means it's worth putting on sunscreen more often than you currently do.

比方說，或許這表示你應該擦比現在更多的防曬乳。

If nothing else, though, the good news is that researchers are at least aware that there's a problem here, and they've been working on protocols to hopefully get more consistent results.

撇開其他的不說，好消息是研究者們至少有意識到這個問題，並且他們在努力調整規範希望可以得到更準確的結果。

Their ideas include using robots that spread sunscreen evenly in all conditions and shifting towards standardized in vitro testing using chemicals in a dish — no human skin involved.

他們的想法包含使用機器人在各種情況下將防曬乳均勻地噴灑，以及朝向標準化的體外測試，在培養皿中使用化學物質 - 不使用人類皮膚。

This will let scientists get way more data points and will improve accuracy.

這能夠使科學家得到更多資料點並提高準確度。

At the end of the day, SPF can be a helpful way to understand what you're buying.

不管怎麼說，SPF 可以幫助你理解你所購買的東西。

To make an informed decision, you just need to know what it says and where those numbers are coming from.

在下一個有根據的結論前，你只需要知道它代表什麼以及這些數字是從哪來的。

And it's also worth knowing that not all hope is lost, either.

另外你也需要知道，這並不是完全沒有希望。

Even if this is a bit of a flawed system, multiple studies have shown that consistent use of sunscreen, even at low SPF, reduces your risk of skin cancer.

儘管這是個有點瑕疵的系統，許多研究都顯示，持續使用防曬乳，即便 SPF 數值很低，可以降低罹患皮膚癌的風險。

So, it's always worth lathering up!

所以，永遠都值得把它抹上。

If you've ever wished you just didn't have to wear sunscreen — well, I've got some sad news for you.

如果你曾經希望你可以不要擦防曬乳－我有些壞消息要給你。

Almost all amphibians, reptiles, birds, and fish can make their own sunscreen.

幾乎所有兩棲類、爬蟲類、鳥類和魚類可以自己製造「防曬乳」。

Mammals are kind of the odd ones out.

哺乳類卻有點與眾不同。

If you want to learn more, you can watch our episode about the missing sunscreen gene after this.

如果你想知道更多，在這之後你可以收看我們介紹關於消失的防曬乳基因影片。