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  • Hey! This episode was sponsored by Head & Shoulders.

  • A hundred and twenty-five million years ago in what is now China, dinosaurs walked the earth.

  • and a few species of small feathered dinosaurs climbed trees

  • This is Sinornithosaurus

  • Although they couldn't truly fly, they could glide, which helped them evade predators and catch prey

  • What makes these dinosaurs unique is how well-preserved their fossils were.

  • Normally when you find a dinosaur it's just a pile of bones and that's all there is.

  • In between the feathers and the parts of the feather we saw little bits of skin

  • And you can tell that they are skin - they're not just random bits of rock or broken up bone or something

  • because they have a particular kind of cells within the structure

  • which are just like the skin cells that we find in humans today

  • Well, my first thought when I saw these was this is dinosaur dandruff

  • and I was already planning to write the paper with the headline of we have discovered dinosaur dandruff,

  • I thought great.

  • So these dinosaurs may have had the first known case of dandruff.

  • But it certainly wasn't the last

  • Our skin cells are constantly replenishing themselves

  • in fact every second 500 new skin cells are created

  • and as they move up through the outer layer of your skin, the epidermis

  • They flatten out and harden until they fall off one by one

  • In fact over your lifetime you will shed about a hundred pounds of dead skin

  • But we don't really notice this because skin falls off in such tiny microscopic pieces

  • except for some people from some parts of the body skin comes off in larger flakes

  • typically from the skin under the hair the scalp and this is what's known as dandruff

  • Now around half of everyone on earth suffers from it.

  • So there are actually a lot of scientists who study this condition.

  • and I'm flying to Cincinnati to Head & Shoulders headquarters to visit their lab

  • Okay.

  • Do you need a break or something?

  • No, it's funny like 'cause I'm not really sure what I'm getting myself into right

  • No. No.

  • I am going to have my head swabbed

  • Mm-hmm. You are

  • What what is that all about? I mean, this is something you do to people all the time?

  • Oh, yeah. Every day.

  • --You're gonna cotton swab my scalp. --Yes

  • And we're looking for what

  • So we are gonna be looking for the malassezia that is on your scalp.

  • Okay, so what do I need to do?

  • So I need you to have a seat here.

  • Let's see and I just put my head in here?

  • Yeah, put your head face forward. Okay. What I'm gonna do is I'm gonna part your hair.

  • So now I'm gonna take my swab I'm basically gonna grab off your scalp. Mm-hmm

  • So then what I do is I take this

  • These are sticky plates here that I can plate the malassezia on

  • and what I can do is I can add a stain

  • throw this under the microscope and this is the individual cells of malassezia here.

  • Malassezia globosa is a fungus that lives on your scalp

  • it thrives in the warm moist environment under your hair

  • and it is thought to be one of the causes of dandruff. So, how did my swab come back?

  • Well, I have malassezia living on my head.

  • This is actually what the fungus looks like. This is a lawn of the Malassezia globosa fungi.

  • You say a lawn. It's a lawn.

  • So basically you can see those little dots they're all individual colonies

  • and when they grow really close together like that, that's a lawn, Kind of like a bunch of grass

  • Now that I'm close to and actually smell it it smells like bread

  • Yeah, well, you know, it's a yeast

  • You know it's a free, living fungus just like the Saccharomyces that are used to make bread and make beer with

  • So, could you make bread with this?

  • Uh.. No. I wouldn't want to make bread with the yeast off of your scalp. Not right now.

  • -- Have you been tested? -- I've been tested. Yes. -- And what did it come out to?

  • I have a decent amount. So... But we all do. So...

  • It's on everyone's head.

  • It's on everyone's head as long as you have hair. --Right

  • But if everyone has Malassezia, why do only half of us get dandruff?

  • Well Malassezia lives on the oils called sebum secreted by your skin

  • The fungi release enzymes called lipases that break down fat molecules

  • Oh, so this is one of the lipases that Malassezia produces

  • So this is something that Malassezia uses to get food

  • But unfortunately as a byproduct of that it also attacks your scalp

  • because it produces free fatty acids that irritate the scalp

  • for some of us those molecules are perceived as invaders if you will

  • and all the defensive forces that we have will get turned on to repel essentially these invading molecules

  • and those defensive forces end up causing this collateral damage

  • that we interpret as an unhealthy scalp and dandruff

  • One of the scalps defenses is to speed up the turnover of skin cells

  • So instead of taking a month for skin cells to mature and reach the surface they take as little as seven days

  • When you know they get to the surface the adhesive function from one cell to the other hasn't been lost

  • And so they shed as these clumps of skin cells three or four hundred together, which we see as a dandruff flake

  • the dandruff flakes are just an indicator of a fundamentally unhealthy scalp underlying it

  • by any measure you can dream of making

  • Dandruff skin samples show elevated levels of inflammatory cytokines

  • Histamines which cause itching, and blood proteins on the surface of the scalp

  • Indicating that the skin is not acting as a good barrier between your insides and the outside world

  • But it goes even further than that down to the level of gene expression

  • Scientists took swabs from healthy scalps and dandruff scalps and then they extracted the RNA

  • Effectively markers of which genes are being expressed and how strongly

  • and then they compared the two groups

  • and they found that there were nearly 4000 genes which were systematically

  • either up-regulated or down-regulated in the dandruff scalps compared to the healthy scalps

  • for example immune and inflammatory response genes were up-regulated,

  • things like lipid metabolism were down regulated and it all kind of makes sense

  • But now that you know that there's a difference at the level of gene expression,

  • How do you actually treat dandruff?

  • So this is the the lawn of Malassezia.

  • This is the Malassezia with a spot of the Head & Shoulders active put on it

  • The Malassezia just doesn't grow where that Head & Shoulders active actually is

  • These active ingredients can be zinc pyrithione, selenium sulfide, or piroctone olamine.

  • They are controlling the metabolism of those Malassezia cells that are leading to irritating substances

  • so the idea is to suppress their bio activity to some extent

  • so that we're reducing the level of irritating substances on our scalp

  • that trigger the irritation and hyperproliferation and buried destruction that we talked about

  • now that we understand like these clusters in these genes signatures of dandruff is

  • Can we reverse these gene signatures if we treat with Head & Shoulders?

  • So this is the group of dandruff at baseline and these genes are all down-regulated

  • and then these genes are up-regulated

  • You can see if you treat with just a cosmetic shampoo that you really don't make a difference in those genes

  • But if you treat with Head & Shoulders after three weeks

  • This signature looks just like somebody who doesn't have dandruff.

  • And so you're looking at 3,700 genes have all clustered all on here,

  • And you're seeing them flip around. They're going from an unhealthy signature to a healthy signature

  • So Head & Shoulders reduces the Malassezia irritants on the scalp,

  • changing your scalp‘s response, and ultimately reducing skin flakes

  • So unlike dinosaurs, we don't have to live with dandruff

  • But in their case the presence of skin flakes reveals something important about their biology

  • They had evolved warm-bloodedness and hence feathers as a way to keep warm

  • But once they had feathers skin could no longer be shed in one piece like a snake but instead in tiny pieces

  • So in fact, although it's an amusing discovery it actually had quite an important or profound point

  • because it tells us that dinosaurs while commonly called reptiles

  • are on the side of the birds and the mammals in terms of physiology. They were definitely warm-blooded

  • Hey, I hope you learned something from watching this video I certainly learned a lot making it.

  • and if you want to find out more about Head & Shoulders research or about how to get rid of dandruff

  • I will put a link to their website down in the description

  • so I want to say a big thanks to Head & Shoulders for supporting this episode of Veritasium

  • and I want to thank you for washing. Or, watching

Hey! This episode was sponsored by Head & Shoulders.

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B2 中上級

実はフケの原因は? (What Actually Causes Dandruff?)

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    林宜悉 に公開 2021 年 01 月 14 日
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