Hey, I'm Dianna.

You're watching Physics Girl.

Just relaxing here in the shade on this beautiful summer day.

Isn't that right, Derek?

Yeah, that's right.

OK, but you're not even in this video yet, so you just chill.

So a couple of months ago, a few guys got in touch with me and told me that they had access to a UV camera.

Do you know what that is?

Do you know what that is?

Yes.

Yes.

Basically, it's a camera that allows you to see the world in ultraviolet, which meant a few things for me.

It meant that I could see what this looks like in UV.

I could see what your face looks like without any lotion or makeup on in UV.

And I could see how sunscreen shows up on your face in ultraviolet.

And so I said, yes, please do come visit me in San Diego and bring your UV camera.

And so the guys from the very well-made YouTube channel, How to Make Everything, showed up at my house.

And this is what we did.

Yeah, on your pants.

Your pants are so tigress right now.

You're going to have some weird tan lines after this.

I was just thinking that.

This is so crazy.

Oh, they're devil horns.

The bigger the better, if you ask me.

I gotta see this.

Is that showing up?

Oh, yeah.

Oh, yeah.

Nice.

Yeah, that was a fun day.

But I should explain why I'm here with Derek from Veritasium, who is also making a video about the world in UV.

I've been making this video for like a year.

I've been making this video for like a year.

And I'm here to make him finish it.

And I'm here to make him finish it.

But for this video, we're going to cut in a few times to discuss the sunscreen controversies.

There are a lot of misconceptions about sunscreens.

And we're going to clear them up.

Yeah.

But for now, I'm going to turn it over to Dianna in the studio.

Back to you, Diana.

The first thing I wanted to look into was whether different SPFs, that is, sun protection factor, which actually is supposed to indicate how strong the sunscreen is.

But anyways, I wanted to see whether different SPFs of sunscreen look different under UV light.

And then I wanted to compare whether high SPFs, like SPF And then I wanted to compare whether high SPFs, like SPF 100, are more effective than just 100, are more effective than just regular high SPFs, like SPF 50.

Here was my thinking.

With a UV camera, things that look lighter are emitting or reflecting UV light, like the wall behind us.

And things that look darker, like the shirt that I'm wearing, are absorbing UV light.

Which is something that I think you'd want to know when it comes to sunscreen, because UV light, ultraviolet light, of course, is part of the spectrum of light or electromagnetic waves from the sun.

And UV is just on the far side of the violet part of the visible light, rainbow, which means it's a wave that has a shorter wavelength, which means it has a higher frequency than any visible light.

And in the end, it can do more damage to molecules like DNA or to cells.

And as we all know, it's been linked to skin cancer.

So my thinking was that, if you look at your skin with sunscreen on, you should see that UV light is absorbed.

So it should look darker.

And yeah, like, when we put the sunscreen on, it looked like face paint.

We were even able to graffiti the side of the truck with sunscreen.

But of course, you can only see it with the UV camera.

So my hypothesis was that the sunscreen with the highest SPF should look darker with the UV camera.

should look darker with the UV camera.

And so we tested a bunch of different sunscreens And so we tested a bunch of different sunscreens with different SPFs on a grid on my arm drawn with permanent marker.

Here's what we saw.

You can't see anything.

That looks just like a sharpie.

It looks like paint.

Looks like metallic black paint.

Initially, we saw that yeah, the low SPF areas do look less dark.

You can tell they don't seem to be absorbing as much ultraviolet light.

But interestingly, there's not a ton of difference between the 30 to 110 SPFs.

And I've heard this rumor that SPFs above 50, anything really high, doesn't actually do anything more than SPF 50.

So I looked into the scientific literature on this.

And I actually found a study that came out just this year in May 2018 that tested 199 people with SPF 50 and SPF 100 sunscreens.

Over the course of about six hours of sun exposure, the subjects got more sunburnt with the SPF 50.

But they do put a nice little disclaimer at the bottom of the paper that leads you to conclude that more research needs to be done on whether there that more research needs to be done on whether there are more benefits over the long term of using are more benefits over the long term of using SPF 100 versus 50.

Hey, guys.

I just want to pause on this for a second.

Because I still think it's weird that I had this conception that above SPF 50, you don't get any more benefits.

And Derek, let me know what you think about this.

But I-- I think I've figured out where that conception came from.

And I think that it's from a 2011 proposed rule from the FDA, the American Federal Drug Administration-- they proposed a rule that would limit the maximum allowed SPF labeling to 50 plus.

Thoughts?

I also don't think it's strange the conception that the high number sunscreens are all basically equivalent.

When I lived in Australia, people were limited to putting only 30 plus on the sunscreen bottles.

And now, they've moved that up to 50 plus.

But it's still, I think, a good idea.

Because as those numbers increase, you're getting diminishing returns.

So what's the difference between 50 and 100?

Well, it's not really that much.

Because a lot of how effective they are comes down to how much you apply and how well you apply it.

So I think it's just a marketing gimmick So I think it's just a marketing gimmick to say that this is a 75, or this is an 80, or this is a 90. to say that this is a 75, or this is an 80, or this is a 90.

So obviously, SPF and the efficacy of different sun protection factors is still an active area of research.

Anyways, back to the fun day at hand.

When we were looking at the sunscreens with the different SPFs, we tried a different sunscreen with SPF 25 and something weird happened.

It was actually lighter.

Like, really light.

This means that it's not absorbing UV light.

But could it still be sunscreening?

Yes.

If it reflects UV light, which is most likely what's happening here with this sunscreen that has zinc oxide in it, which is a substance that's known to reflect some types of UV light.

So, this is where I got really confused.

I started looking up some sunscreen ingredients and what they do and why some are reflective and others are absorptive.

And I ended up going down the rabbit hole of sunscreen controversies.

I'll get to the discussion on health effects of different sunscreen ingredients in a minute.

But I did find that Hawaii recently banned some sunscreens from the state.

The reason why is that ingredients oxybenzone and octinoxate were found to be contributing to coral reef bleaching, a process whereby coral polyps expel the little algae living inside of them-- actually sounds like an exorcism, but it is, in fact, a bad thing.

So starting in 2021, Hawaii is banning any sunscreens with those ingredients.

This ban was based off of recent research.

Which begs the question, are the health effects and environmental effects of sunscreen ingredients not well known?

OK, I'm just going to pause here again.

Because I feel like this is a good discussion for us.

There is a lot to unpack here.

But I want to start out with that SPF 25 sunscreen that was really reflective.

There's two major ways that sunscreens can protect your skin from UV light.

One of the ways is by absorbing that light and turning that energy into heat.

And another way is by reflecting the light.

And what you saw was clearly more reflection.

Now, in the media, they're often called physical versus chemical sunscreens, which is maybe not the best designation.

I don't think it's the best.

Because they are all chemicals.

Maybe it's a better distinction to say that the chemical sunscreens are organic, because they are organic molecules.

They have these chains of carbon.

And the so-called physical sunscreens are inorganic molecules, things like titanium dioxide and zinc oxide.

So they do a bit more reflection.

But they also do scatter the light.

They absorb the light.

This chemical versus physical distinction bothers me, as you know.

Because I think it's used in a misleading way on a lot of health blogs and in a lot of media indicating you should avoid these chemical sunscreens because they're chemicals.

You don't like it.

I don't like it.

Because they're all chemicals.

Right.

Everything's a chemical.

Right.

I think there is a deeper reason why people would say chemical versus physical, because chemical could describe, by virtue of its chemistry, that's how it interacts with the light.

Whereas, a physical sunscreen, by virtue of its structure, is really how it interacts with the light.

You're right when it comes to the marketing, people do try to use the chemical label as a negative term.

And I think that it actually hides an important discussion about the potential safety issues of what they call chemical sunscreens.

So we're discovering things about sunscreen ingredients all the time.

For example, recent research has shown that some sunscreen ingredients-- and in particular, some of the organic sunscreen ingredients-- can get into the bloodstream and into breast milk through your skin, which led the FDA to recently state that this is a significant discovery that needs to be considered as we continue to evaluate the health and safety of sunscreen ingredients.

In fact, the FDA just recently rejected eight new proposed sunscreen ingredients.

Because they felt there wasn't enough science to show that these ingredients were safe.

But my question is that, now that we know sunscreen ingredients can enter the body through the skin, should we be looking back at those 16 ingredients?

Should we be looking at them through the lens of the new research and judging them with the same thoroughness that we're judging these eight new ingredients against, for example?

What's surprising to me is that there is still so much to be learned about sunscreen.

I think it's a little weird because on the one hand, you're saying these health blogs are saying chemicals bad.

But on the other, you're saying, well, maybe chemicals are bad, because they haven't been really tested yet.

That's not why people are saying that they're bad.

And in fact, some of them may be perfectly fine, and they get lumped in with the ones that do have, that do cause skin allergies.

Like, to say because they're chemicals is the reason, you might lose out on potentially a ton of great sunscreen ingredients that are going to be really effective for protecting the populace against skin cancer.

But people have lumped them into this chemical category, But people have lumped them into this chemical category, which really just means organic molecule category.

which really just means organic molecule category.

Maybe we're going to find ones that don't get absorbed into the bloodstream as readily.

You know what I mean?

Yeah.

There is so much to be learned.

But at the end of the day, I think, put on the sunscreen.

At the end of the day, do you want skin cancer?

Because it is the most common cancer in the US.

You heard it from the man.

Wear sunscreen, kids.

Oh, yeah, also thank you for watching this video.

And check out Derek's video, which is going to be about-- The world in UV.

Something about sunscreen, but about everything else, too.

Really cool experiments that we filmed yesterday.

Check out the video by the How to Make Everything guys.

They made sunscreen in the end.

Did they?

Yeah.

Awesome.

Thanks so much for watching, and happy physics-ing.