SUNSCREEN in UV

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Creator: Dianna Cowern
Videography: Chris Peck, Dianna Cowern, Derek Muller and Eric Birkemeier
Editing: Jabril Ashe

Thanks to Dan Walsh, and congratulations on his PhD!

Thanks to Kyle Kitzmiller and Unicorn Snot

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Resources and Further reading:

“The Food and Drug Administration (FDA) is proposing to limit the maximum labeled SPF value for over-the-counter (OTC) sunscreen drug products to ‘‘50+.’

NYT Article on SPF 50

FDA: Understanding over the counter sunscreens

Sunscreen Penetration of Human Skin and Related Keratinocyte Toxicity after Topical Application

Regulatory Policy Information for the Sunscreen Innovation Act (information on FDA’s rejection of new sunscreen ingredients)


Sunscreen + coral reefs

”SPF 100 vs 50 study”

Screenshot of “health blog”

Overview of suncreen ingredients

“Titanium dioxide and zinc oxide provide UV protection primarily via absorption of UV radiation and not through significant reflection or scattering.”

From the FDA’s website:
“Although the protective action of sunscreen products takes place on the surface of the skin, there is evidence that at least some sunscreen active ingredients may be absorbed through the skin and enter the body”

In 2014, the FDA updated sunscreen ingredient proposal rules

[masterminstrel]

What would've been cool is if you'd filmed in UV the affects of going in water with sunscreen on, or maybe a time lapse to show how much it fades throughout the day.

[kfitch]

"At the end of the day, put on sunscreen" -- uhhh wouldn't it make more sense to put it on at the beginning of the day? 😀

[jefferylegere]

I had a discussion not long ago where I was in favor of including UV cameras in cell phones for creative purposes and others saw no benefit to having them. This would be a great use for them, you could see if you had applied your sunscreen properly.

[QyetOne]

One thing I'm surprised went unmentioned:
"SPF" is defined by a testing method, where the SPF number is the threshold of how much UVA/UVB doesn't make it through the product (applied in a standardized layer). It's a very simple bit of math!
SPF 4 = 1/4 or 25% of the radiation is not blocked (absorbed/reflected)
SPF 8 = 1/8 or 12.5%
SPF 15 = 1/15 or 6.7%
SPF 30 = 1/30 or 3.3%
SPF 50 = 1/50 or 2%
SPF 100 = 1/100 or 1%
SPF 150 = 1/150 or 0.67%
So it makes good sense that you can't readily tell the difference at higher SPF's because the difference is getting tinier and tinier. The difference between SPF 15 and 30 is 3.4% radiation getting through, but the difference between 50 and 150 is only 1.3%. This is also interesting in terms of evaluating the UV camera's receptivity, because SPF doesn't discriminate between how it gets results (absorbing vs reflecting), but the camera is registering the UV radiation emitted/reflected, so as you observed absorption darkens and reflection may be invisible or actually lighter. So if you had two different brands achieving the same SPF value by different combinations of the two mechanisms, they may appear different on the camera even though they have the same efficacy from the skin's point of view.

[veritasium]

I love how on the day we filmed this I got sunburned because I couldn't wear sunscreen or else it would show in the UV camera. I like that my stealth filming of you telling us how you really feel made it into this video. Also, why do I look so serious? Happy Physicsing Dianna!!

[EmmanuelGoldstein]

I have always heard the two sunscreen categories described as "chemical" and "mineral." I don't think the chemical bit is an intent at scaring people. It's just descriptive of how the sunscreen works. When in the video they say that these types of sunscreens "absorb" the UV light, what they really mean is that the UV light induces a chemical reaction within those chemicals, where they are broken down into smaller molecules. By giving energy to the chemical reaction, the light becomes less dangerous, and its frequency shifts down so that it is mostly heat rather than penetrating rays. And this is why they say you have to reapply the sunscreen every few hours: the chemicals get consumed as they work. They also get consumed if the sunscreen in left in a hot location, so it's best to not leave your tube of sunscreen out in the sun when you're at the beach. The mineral sunscreen, on the other hand, are physical barriers that are placed between the light and the skin. No chemical reaction takes place (or only a tiny one). The light simply bounces off it. This is also why you can generally see mineral sunscreens on people's skin. It's an actual physical barrier. But they also make tinted varieties that are less noticable.

Both chemical and mineral sunscreen contain chemicals that are potentially toxic to some degree. The chemical sunscreens we use in the US are banned in Europe and vice versa. (But this might also just be protectionism because the chemicals in European sunscreens are produced by European companies, and the US sunscreens' are made by US companies). However, the molecules in mineral sunscreens are orders of magnitude larger than those in chemical sunscreens, and the latter get broken down into even smaller ones. So the chemicals in chemical sunscreens are much more likely to make it into your bloodstream than those from mineral sunscreens.

Regarding effectiveness, my understanding is that the chemical ones tend to work somewhat better, although they need to be continuously reapplied because the UV light is constantly breaking them down. With mineral sunscreens you also have to make sure that they have BOTH zinc oxide and titanium dioxide in them, as the two minerals are effective against different light wavelengths. My personal sunscreen strategy is to use a mineral sunscreen as my every day walking about sunscreen. I mix an untinted and tinted so that it matches my skin color. If I'll have a long sun exposure, then I have a sunscreen that is primarily mineral but also contains some of the chemicals. To me that seems the best tradeoff between safety from the sunscreen vs safety from the sun.

[Hepcat]

There’s a plant called Heracleum, which is pretty common in Russia (and the whole northern hemisphere if the Wikipedia is correct). It’s very invasive and grows very fast. If not destroyed it can cover very large areas very fast. What’s worse is that its juice causes severe burns. That’s common knowledge in Russia. A much less known fact is that those burns are not caused by juice itself. These are actually sunburns. The plant’s juice causes chemical reaction which dramatically increases skin’s photosensitivity. So it’s basically a reverse sunscreen. And those severe (sometimes even lethal) burns can be avoided just by covering from sunlight.

[Ema-fmzy]

I don't get why people think inorganic is bad and organic is good. Poison can be organic as you can get it from snakes, scorpions and animals like that. Water is inorganic, air is inorganic. People really nead to understand what can do damage, to who and in what quantity. It's like I'd be against using peanuts for any purpose because some people are allergic.

[WaterdropGirl]

Stay strong Diana! We hope you feel better soon!

[davidmaes]

At 10:28 Derek says "At the end of the day, put on the sunscreen".
Bad advice.

I would put it on at the beginning of the day. :-D

[physicsgirl]

OH MAH GARSH. Benoît, you are very correct. FDA stand for Food and Drug administration. Apologies for the error, all.

[TyBraek]

I was super surprised at the spray sunscreen. I always thought they feel like they cover, but aren't covering as well as normal lotion.

[htme]

Thanks for helping us with our experiment and trying on the sunscreens, it was a blast!

[Mr._Du]

the best sunscreen is staying inside to watch physics girl and veritasium videos all day

[dzhjjoh]

Can’t help but sing “THE SUN IS A DEADLY LASER”

[pomodorino]

9:39 And that's why it is important to spread scientific literacy as much as possible.
Thanks Dianna for your work! (and thanks Derek also, I'm a great fan of him as well)

[Tribul]

Disappointed that no distinction was made between UVA and UVB.

[arianne]

Uhmm I think FDA stands for “food and drug administration” not “federal drug administration” 4:56
I love the video though❤️

[NewMessage]

SPF is also the noise you make when you accidentally open your mouth when spraying sunscreen on your face.

[nathanalday]

The title card for the video, with Dianna's face split down the middle between UV and visible light, is a work of art and would make a great poster.