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Jen Oliver: welcome to the, so that's
Why podcast, where we unpack the

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science behind everyday questions.

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I'm Jen.

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Chris Smith: I'm Chris.

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Jamie Eynon: And I'm Jamie.

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Jen Oliver: Okay, so hands up if you've
ever pulled out a single strand of hair.

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Held it up to the light and
thought, when did that happen?

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Why does our hair turn grey?

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Because it's one of the most visible
changes our bodies go through, and

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yet most of us have no idea what's
actually going on beneath the surface.

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Jamie Eynon: It

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really is.

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And can we talk about the universal
panic of finding your first grey hair?

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You spot one in the mirror and suddenly
you're doing a full scalp inspection

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like you're searching for contraband.

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Then you are texting your mates
asking when they started trying

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to work out if you are ahead
of schedule or behind schedule.

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Jen Oliver: I remember my first grey hair.

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I was convinced it was just a trick of
the light, and so I actually moved to

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about three different mirrors before I
accepted that it was well and truly white.

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Chris Smith: And here's something
that might surprise you, that your

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hair doesn't actually turn grey.

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It grows grey.

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So every single strand of hair
starts off completely white

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before pigment gets added.

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So when we say our hair turns grey,
what we actually mean is the pigment

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system has stopped doing its job.

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Jen Oliver: So it's such a good
distinction that be So the color

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we see is essentially being painted
on during the growth process.

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Chris Smith: Exactly right.

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So we have specialized cells called
melanocytes, and they sit inside

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each hair follicle and they inject
pigment into the hair as it grows.

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And there are two types of pigment.

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We've got you melanin, which
gives you the black and brown

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shades and fear melanin, which is
responsible for blonde and red tones.

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Your unique combination of those two
determines your natural hair color.

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Jamie Eynon: Hold on.

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That's actually kind of amazing.

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Thousands of tiny cells are just
deciding what color our hair should be,

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Chris Smith: exactly a hundred thousand
of them to be exact on the average head,

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Jen Oliver: I wonder who
actually counted them.

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Each of them goes through
repeated growth cycles as well.

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Melanin, it's regenerated at the start of
each new cycle, but after roughly seven

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to 15 of those cycles, the production
starts slowing down, doesn't it?

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So there's almost a built-in
limit to the coloring.

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Jamie Eynon: 15 cycles.

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Sounds like a lot though.

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How long is each cycle?

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Chris Smith: So it's anywhere between two
to seven years, depending on the person.

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So the maths is different for
everyone, but eventually the pigment

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production starts winding down.

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Jen Oliver: Now, here's where
a recent research has changed

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our understanding significantly.

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So there was a study published in Nature
that revealed something incredible about

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the stem cells responsible for hair color.

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Why don't you tell us more, Chris?

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Chris Smith: Yeah, so this really was
an important piece of research and

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what it told us was that melanocyte
stem cells, which are the parent

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cells that produce your pigment making
melanocytes, are uniquely mobile.

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They normally shuttle back and forth
between different compartments within

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the hair follicle in one follicle
compartment called the bulge.

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They sit dormant in another,
uh, called the hair germ.

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They receive chemical signals from
proteins that tell them to mature

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and start producing pigments.

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Jen Oliver: And the key finding was that
as hair ages and the cycles repeatedly,

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these stem cells start getting physically
stuck in the dormant compartments.

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So they start migrating to where
the make pigment signals are.

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So they never get the instruction
to actually produce the color.

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Jamie Eynon: So it's not that
the cells actually die, they're

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just stuck in the wrong place.

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That's like having all the ingredients
for dinner sitting in the cupboard,

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but nobody's walking to the
kitchen to actually start cooking.

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Chris Smith: Yeah, that's a
fair way to look at it actually.

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Um, and it's been described
as those stem cells losing

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their chameleon-like function.

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And this is actually encouraging
though because stuck cells

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are potentially fixable.

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Dead cells aren't, of course,

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Jen Oliver: but there's a second
mechanism at work who isn't there.

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And this one involves something you'd
normally associate with bleach in your

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hair, and that's hydrogen peroxide.

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Chris Smith: Absolutely.

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Right.

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And your hair follicles contain, um,
and produce small amounts of this

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hydrogen peroxide naturally as a
byproduct of normal cell activity.

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So under healthy conditions, an
enzyme called catalyze, breaks it

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down into harmless water and oxygen.

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But as we age, catalyze levels
decline so that hydrogen peroxide

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builds up and starts interfering
with the pigment production process.

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Jen Oliver: And researchers at
the University of Bradford, they

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confirm this when they analyzed
pigmented hair versus grey hair.

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So the grey and white hair
samples contained high

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levels of hydrogen peroxide.

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Whereas the pigmented hair had
none, so effectively, your hair

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is being bleached from the inside,

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Jamie Eynon: so your own body is giving
you highlights without your permission.

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That explains why grey hair often
has a slightly different texture too.

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It's been chemically
altered at its source.

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Mm,

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Chris Smith: it does.

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And the hydrogen peroxide doesn't
just block pigment production.

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It also damages the repair mechanisms
that would normally fix the problem.

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So it's created a
compounding effect over time.

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Jen Oliver: Now one of the most
interesting areas of research has

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been around stress and greying.

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So we've all heard that phrase,
or you're giving me grey hair or

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you're gonna tear my hair grey.

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But there's actually science
behind it, isn't there?

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Chris Smith: There is, and it's
a fascinating piece of work here.

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So in 2020, researchers at Harvard
published a study that provided.

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The first definitive, uh, mechanism
linking psychological stress to grey hair.

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Jamie Eynon: So stress generally
does make your hair go grey faster.

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Chris Smith: Yep, it does.

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And what the Harvard team found
was that under acute stress, the

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sympathetic nervous system, that's
your fight or flight system,

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releases a burst of norepinephrine
directly into the hair follicle.

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And this causes a dormant melanocyte
stem cells to activate prematurely,

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rapidly, use themselves up, and
then they're gone permanently.

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Jen Oliver: And genetics play
a huge role too, don't they?

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Of course.

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In how quickly you go grey.

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There was a study of over 6,000
people with diverse Latin American

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ancestry, and they identified a gene
called the IRF four as the first gene,

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specifically associated with hair greying.

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So that gene is estimated to account for
about 30% of greying with the remaining

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70% down to age stress environment.

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Jamie Eynon: So nearly a third of
your grey hair timeline is written

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in your DNA before you are even born.

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That's reassuring or deeply annoying
depending on your family photos.

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Jen Oliver: Yeah, there's nothing
quite like a family album to give you

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a preview of the coming attractions.

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Chris Smith: Yeah.

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There are ethnic patterns too.

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So people of European descent tend to
start greying in their mid thirties.

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Um, those of Asian descent.

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In their late thirties and people
of African descent a bit later.

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So typically in their mid forties.

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Jen Oliver: And then there's
premature greying, and that

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varies as well, doesn't it?

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So before 20 for Caucasians,
before 25 for Asians, and before

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30 for people of African descent,

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Jamie Eynon: right?

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So going grey at 28 might be
premature in one group and

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completely normal in another.

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It's another example of why universal
health benchmarks don't always work.

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Chris Smith: Yeah, definitely.

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And for premature greying, specifically,
nutritional deficiencies are a

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factor that's often overlooked.

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So, uh, vitamin B12 is particularly
important 'cause that supports

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melanocyte function and deficiencies
one of the most common nutritional

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causes of early greying.

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So studies have found significantly
lower B12 levels in people

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experiencing premature greying.

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Jen Oliver: I wonder how many
people are now adding B12 to

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their, their shopping basket.

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Copper's another one, isn't it?

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It's a co-factor for Ty Roese, and that's
the key enzyme in melanin production.

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So if you've got low copper levels,
that's been directly linked.

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With premature grey in iron and zinc
and even vitamin D and calcium have

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also been flagged for research too.

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Jamie Eynon: So if you are going grey
earlier than expected, it might be worth

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checking your nutrient revels rather
than just blaming your grandparents.

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Chris Smith: Yeah, that's right.

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And, and in some cases, addressing
the deficiency through diet

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or supplementation may help.

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Slow further greying.

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It's worth noting that reversing
existing grey hair through

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nutrition alone is uncommon.

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The biggest benefit is in
preventing further progression.

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Yeah,

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Jen Oliver: but the practical
side of this, it's actually quite

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encouraging though, isn't it?

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Because while we can't change
our genetics, we can absolutely

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influence the nutritional and
lifestyle choices that we make.

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So making sure we're getting enough B12,
maintaining good iron and copper levels,

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managing stress, getting enough sleep.

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I mean, these are all things
within our control that affect the

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biology we've been chatting about.

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Jamie Eynon: Yeah, so basically eat well.

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Sleep well, stress less
and your hair might.

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Thank you for it.

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Simple said no when living
in the real world ever.

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But knowing the reasons behind it does
make you take it a bit more seriously.

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Jen Oliver: Yeah.

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And there are some other factors
that can accelerate things.

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So smoking's been associated
with premature greying.

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Um, thyroid disorders can
disrupt the melanocyte function.

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And there's also some autoimmune
conditions that attack

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the melanocytes directly.

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Jamie Eynon: So what
about reversing grey hair?

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Is it actually possible or are we firmly
in the wishful thinking territory?

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Chris Smith: So it's not as
far fetched as it once sounded.

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The NYU finding that GE mentioned
earlier that stem cells get stuck

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rather than die is significant because
it suggests that if we could persuade

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those cells to start moving again,
pigment production could theoretically.

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Jen Oliver: There have been documented
cases of individual grey hairs naturally

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re darkened into which shows that the
process, it isn't always a one-way street.

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There was a small study in 2025
and they explored rose stem cell

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derived exosomes as a treatment, and
a hundred percent of those patients

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achieve significant improvement.

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But the research is still in
its very early stages, so.

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So what's this space?

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Jamie Eynon: So, so we're not
there yet, but the door is open.

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Uh, that's more hopeful
than you would've thought.

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Jen Oliver: Yep.

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And some medications used in cancer
treatment, they've also been observed

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to trigger hair re pigmentation
as a side effect, which has given

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researchers additional clues about
which biological pathways are involved.

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Chris Smith: Yeah, that's right.

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And the, the closest someone is
to the early stage of greying

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before that stem cell pool is fully
depleted, the better the chances

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of any future treatment working.

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So there is a reason to be optimistic.

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Jen Oliver: Indeed, there is.

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So to answer our question,
why does our hair turn grey?

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Chris Smith: So hair turns grey because
the melanocyte stem cells responsible

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for producing pigment gradually
lose their ability to function.

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They can become physically stuck
in the wrong parts of the follicle

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hydrogen peroxide buildup and
disrupt pigment making machinery.

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Stress can deplete the stem cell reservoir
through the fight or flight response.

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And genetics set the overall
pace of this greying process.

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Jamie Eynon: So your grey
hairs aren't a sign of failure.

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They're a sign that roughly a hundred
thousand tiny pigment operations have

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been running successfully for decades, and
some of them are finally coming to an end.

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Jen Oliver: So that's
why your hair turns grey.

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It's a combination of stem cell biology,
oxidative chemistry, your nervous

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system, your genes, and even your
nutritional status all working together.

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And the exciting part is that researchers
are closer than ever to understanding

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whether some of it might be reversible.

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That's it for this week.

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Make sure you hit that subscribe button.

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We're unpacking the science behind
everyday questions each week.

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Tell us in the comments what
you'd like us to explore.

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Thanks for geeking out with us,
but for now, that's it from me.

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00:11:44,500 --> 00:11:45,280
Jamie Eynon: That's it from me.

236
00:11:45,490 --> 00:11:46,125
Chris Smith: And that's it from me.

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Jen Oliver: Bye for now.