Name: What Actually Causes Dandruff?
Uploaded: 2020-03-28T18:20:46.000Z
Duration: 9 min 2 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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

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,

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

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

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

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

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

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

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

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

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.

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

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

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 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

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 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,

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