Name: What Causes Dandruff?
Uploaded: 2026-01-12T13:46:33.000Z
Duration: 5 min 40 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...

It is one of the most common and annoying human experiences.

You're wearing a black shirt, you look in the mirror, and

For centuries, we've tried to scrub it away.

We've blamed it on bad hygiene, dry weather, or cheap shampoo.

Dandruff actually has very little to do with how often you wash your hair.

In fact, that white flake on your shoulder is the result of a microscopic war taking place right now on top of your head.

It involves an invisible jungle, a hungry fungus, and

a chemical reaction that half the population is allergic to.

Welcome to Simple Things: Surprising Histories.

Today, we are looking at the biology under your hat.

To answer the question, what actually causes dandruff?

Before we meet the villain of this story, we have to clear up a massive misconception.

Most people think dandruff is just dry skin.

But biologically speaking, it's usually the exact opposite.

True dandruff thrives in an oily environment.

That is why you rarely see dandruff on young children.

They haven't hit puberty yet, so their oil glands aren't fully active.

Here is what's happening on a cellular level.

New cells are born at the bottom layer, and

they slowly travel to the surface to replace old ones.

On a healthy scalp, these old cells float away one by one.

They're so small that you can't see them with the naked eye.

But with dandruff, these cells don't float away alone.

They stick together in clumps of hundreds, cemented by oil.

When the clump gets big enough to be visible and falls off, that's the flake.

So if it's not just dryness, what is causing these cells to clump and fall so frantically?

To understand the cause, we have to zoom in, weigh in.

And it has a climate, the temperature and sweat.

Every human being on Earth hosts a microbiome on their scalp.

It's a mix of bacteria and fungi that live there permanently.

It sounds a little unsettling, but it's perfectly natural.

In fact, these microbes have evolved alongside us for thousands of years.

However, there is one specific resident in this scalp jungle that causes all the trouble.

It's a yeast like fungus with a fancy name, Malassezia globosa.

Malassezia is on everyone's head right now.

But for about 50% of the population, this fungus triggers a chain reaction that ruins the party.

The Malassezia fungus is hungry, but it's a very picky eater.

the natural oils produced by your sebaceous glands to keep your hair shiny and protected.

The fungus feasts on these oils, but it doesn't digest everything.

It breaks the oil down and leaves behind a byproduct called oleic acid.

The fungus eats the oil and poops out oleic acid directly onto your scalp.

Roughly half of the people in the world are sensitive to oleic acid.

If you're in that 50%, your body views this acid as an irritant.

And when the human body thinks the skin is under attack, it has one main defense mechanism.

To get rid of the irritant, your scalp hits the accelerator.

In a normal, healthy cycle, skin cells take about a month to mature, travel to the surface,

But when your scalp is irritated by oleic acid, it speeds up this process drastically.

Instead of one month, the skin tries to turn over in just two to seven days.

The the cells are pushed to the surface before they are fully dead or ready to separate.

They arrive in a panic, still oily and sticky, clutching onto their neighbors.

These massive clumps of rushed cells are what you see on your collar.

So when you use an anti-dandruff shampoo, you aren't just cleaning the hair.

medicine designed to reduce the population of molassezia so the acid production stops and your skin can calm down.

So the next time you see those white flakes, remember, it's not because you're dirty.

It's because you have a highly active ecosystem.

You have a hungry fungus, plenty of natural oil, and

a body that is just trying a little too hard to protect you.

It's a complex biological battle happening right on top of your head.

I hope you enjoyed this peek into the microscopic history of everyday life.

If you learned something new, please hit that like button.

It really helps the channel and subscribe to Simple Things: Surprising Histories for more surprising stories about the world around us.