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At age 44, Xie Qiuping cut her hair
for the first time in over three decades.
At the time, her impressive locks
extended over five meters—
earning the Guinness World Record
for the world's longest hair.
But even with this record-setting feat,
her hair might not have reached
its maximum possible length.
So just how long can human hair
actually grow?
To get to the bottom of this question,
let's start at the bottom
of a hair follicle.
Follicles are tube-shaped structures
nestled roughly half a centimeter
below the skin's surface.
At their base is what's
called the hair bulb,
and it contains rapidly
dividing matrix cells.
As they divide, these develop into
specialized hair cells called trichocytes,
which harden as they fill themselves
with cable-like keratin proteins.
As more and more trichocytes are produced,
they form a strand of hair that emerges
from the follicle and grows upwards.
All the hair on your body grows this way,
but not all hair will grow
to the same length, shape, or color.
Those properties are determined
by yet another type of cell
within the hair bulb:
the fibroblast.
Fibroblasts instruct the matrix cells
to grow specific kinds of hair
for each part of the body.
This is why doctors doing hair implants
usually use follicles
from the same body part,
though they'll sometimes change things up.
For example, eyelashes are some
of the shortest hairs on your body
at an average length of one centimeter.
So to give people longer eyelashes,
doctors might implant scalp follicles,
which grow at a rate
of about 15 centimeters per year.
So these patients will have to trim
their new lashes regularly
to avoid a blinding curtain of hair.
In general, our follicles
are very resilient.
Even if you pluck hair out
with your fingers or some wax,
you’ll likely only damage matrix cells,
not fibroblasts.
So given time, those hair bulbs
will repair themselves
and begin producing new hair.
However, each strand of hair
will only grow for so long.
We don't fully understand
how follicles measure time,
but in most cases they'll stop
growing a strand after 5 to 7 years.
This means that at the rate
of 15 centimeters a year,
the average person’s scalp hair
could reach a maximum length
of around one meter.
The precise duration and speed of
hair growth varies from person to person
depending on genetics, hormones,
and various health conditions,
and it’s difficult to know exactly what
combination of these factors
let Xie Quiping reach her record.
But however long your locks may be,
when a follicle stops growing,
the hair falls out—
shedding from our heads slowly,
or in clumps during showers
and hair brushing.
After a hair is lost, fibroblasts will
trigger the growth of a new strand
to fill out your scalp— usually.
As we age, follicles run
out of certain cell types,
which can lead to changes in hair growth.
For example, when they run out of
pigment-producing melanocyte stem cells,
follicles begin producing gray hairs.
And since there are only a handful
of melanocyte stem cells per follicle
to begin with,
they tend to run out relatively early
in a person’s life.
Similarly, when follicles run
out of epithelial stem cells,
they begin to shrink and grow
shorter, thinner strands
before eventually shutting down
production altogether.
This is what leads to baldness,
though the condition can also be
accelerated by testosterone,
which can prevent
fibroblasts’ instructions
from reaching a follicle’s cells.
While it’s completely natural
for hair growth
to change over the course of our lives,
there are ways to take more control
of our scalps.
Some baldness remedies
remove excess testosterone,
and special shampoos can address
the coarse, brittle strands
reported by many people with gray hair.
Since our bodies already produce hair
at the fastest possible biological speed,
there's currently no way
to grow hair faster.
But even if you’re unlikely to beat
Xie Qiuping’s record,
with time, the right treatments,
and some genetic luck,
you should be able to grow
some luscious locks of your own.
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