What Actually Causes Dandruff?

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 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 it 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. Those defensive forces end up causing this collateral damage that we interpret as an unhealthy scalp and dandruff. One of the scalp's 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 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. 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 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 bioactivity 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 these clusters and these gene signatures of dandruff, 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 that have all clustered 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.