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It looks like I'm wearing
really bad tanning oil.
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?
 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 the 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.
 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
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.
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
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
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,
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.
 Yeah.
 I'll watch that.
 I will link both of those
videos in the description
and at the end of this
video or whatever.
Thanks so much for watching,
and happy physics-ing.
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 It's cool.
You have a tagline.
I don't have a tagline.
 I know.
Yeah, but it's
happy physics-ing.
 It's still pretty
good, though.
No one's going to steal that.
Bazinga.
 You know, someone
tried to steal it once.
And I was like, you can have it.
