Kind: captions
Language: en
this is me at the end of college so
anyway so today I'm packing up my room
is absolutely disgusting uh there's dust
all over the place unbelievable how much
dust this place accumulates just unreal
21 year old me was apparently fascinated
by dust but where does it all come from
well in this video we are going to get
to the bottom of this now this video was
sponsored by Google and when they
approached me about sponsoring a video I
suggested I show you how I use Google to
research a complex question after all
research is just research anyway I
couldn't pick a simple question like how
far away is the Moon how old is Derek
Muller or how much wood could a
woodchuck chuck if a woodchuck could
chuck wood because the video would be
over already but in the space of all
possible queries questions like these
with clear and ambiguous answers are by
far in the minority in fact of all the
billions of search queries typed into
Google every day fully 15 are ones that
Google has never even seen before so
Google never actually gives you answers
instead in just a fraction of a second
it uses algorithms to select the most
relevant information from the hundreds
of billions of web pages it has indexed
what you do with that information is up
to you so for this video I intentionally
selected something surrounded by Miss
dust unbelievable so a while back when I
was filming a different video a PhD
scientist told me you know 70 of
household dust is dead skin and I'd
heard that before and chances are you
have two if you type is dust into Google
the top autocomplete result is dead skin
because that's one of the most common
ways people complete that query but a
quick scan of this page suggests that
the claim is not true it's a
misconception from Live Science
sometimes a specific percentage of dust
is said to be dead skin usually about 70
or 80 percent but unless you're a
molting bird or a reptile or you work in
Dr Frankenstein's laboratory very little
of your environment is composed of dead
body parts or BBC Science magazine which
asks what is dust made of think it's
human skin think again the article says
it's a misconception that it's mostly
from outside the rest is carpet fluff
and clothes fibers and sure enough all
over the web you'll find people
debunking idea so is that it case closed
hardly I mean I'm not just gonna do one
search and call it a day it's important
to be aware of your own biases when I
started this search the claim seemed
false the idea that 70 to 80 of dust is
dead skin it's exactly the sort of thing
that is gross enough to spread as an
urban legend but it just seems
implausible I mean if most dust is dead
skin then why do abandoned buildings get
dusty over time the debunking claims fit
my preconceptions so it would be easy to
stop here but you got to be careful not
just to search to confirm what you
already thought a common mistake people
make is putting the answer they are
looking for right in the search query
looking more closely these websites lack
scientific papers as references and I'm
curious if the idea that 70 to 80 of
dust is dead skin if that's totally
wrong then how did the myth get started
in the first place surely some dust must
be dead skin but how much well the good
strategy is to start broad how do you
define dust exactly well dust is
generally defined as particles that can
become airborne for a significant period
of time when perturbed by natural forces
but how long is a significant period of
time and what are natural forces exactly
so the definition of dust has fuzzy
boundaries kind of like dust itself
if you ask the question how big is a
dust particle you get different answers
the international standardization
organization defines dust as any
particle smaller than 75 micrometers in
diameter that's roughly the width of a
human hair the glossary of atmospheric
chemistry terms includes anything up to
100 micrometers but I've found several
papers that include particles as large
as two millimeters this large
discrepancy is due to the fact the most
important property of a dust particle is
not its size but its settling velocity
which then determines how long it can
stay airborne a 100 micrometer metal
ball would fall to the ground very
quickly while a two millimeter long
cotton fiber could float on indoor air
currents indefinitely so to get around
the different sizes shapes and densities
of dust particles the international
standardization organization has a way
of calculating an effective diameter
they Define it as the diameter of a
hypothetical sphere of density one gram
per centimeter cubed having the same
terminal settling velocity in calm air
as the particle in question regardless
of its geometric size shape and true
density
buy any of these metrics a single human
skin cell with an average diameter of
around 30 micrometers would count as
dust so then how many dead skin cells
are we shedding you'd think the average
rate of skin shedding would be well
established but the internet is a
tangled web of misquotations and missing
citations when it comes to skin in
trying to answer this question I found
dozens of web articles saying we shed
anywhere between 30 000 skin cells per
day to 300 000 skin cells per minute and
estimated weights of dead skin as high
as nine pounds a year per person
using Google Scholar a great resource
for searching published scientific
research I was able to track down
several peer-reviewed sources that
agreed on the numbers
every hour you create about 20 million
new skin cells as those new skin cells
form they push older cells up through
the layers of the epidermis and over a
period of weeks they flatten out and
Harden forming the barrier that protects
our bodies from the outside world
ultimately these dead skin cells fall
off usually one by one for healthy skin
so we are constantly molting like a
snake we just don't notice it because
our skin comes off one cell at a time
fun fact dead skin cells are shed more
rapidly from your forearms than from
your back and more rapidly from your
back than from your abdomen and one of
the ways scientists have measured these
rates of skin shedding is actually by
taping containers onto people's skin
and collecting up the dead skin cells
shed over at least a 48 hour period
yeah I'm gonna regret this
based on these measurements we know that
each Square centimeter of your body is
shedding around a thousand dead skin
cells per hour
now the average adult body has a surface
area of nearly two square meters meaning
you are shedding nearly 20 million dead
skin cells per hour that adds up to half
a billion dead skin cells per day now
half a billion dead skin cells weigh
between one and two grams that's just a
little bit less than the weight of a
penny
over a year that means you should half a
kilogram or over a pound of dead skin
if you want to think about it another
way in a single year you give off around
180 billion dead skin cells that's
roughly the same number as there are
stars in our Milky Way galaxy
an average family of 2.6 people could
cover the entire horizontal surface of
an average 2 000 square foot home with a
layer of skin cells one cell deep in
around 200 days that is assuming all
their dead skin cells accumulate around
the house which of course is not true
some will come off in the shower and
some will get captured in clothes and
bed sheets and be rinsed out in the wash
not to mention dead skin cells shed
outside the home
still the amount of skin we shed is not
small but how much is it as a percentage
of household dust
well that turns out to be a trickier
question because there are a lot of
other sources of dust like pollen fibers
from rugs clothes and Furniture dirt
from outside even micro meteorites dust
from space
[Music]
to clear things up I called around to
some dust experts and they pointed me to
this book house dust biology by Johanna
van Brunswick from 1981. and sure enough
on page 37 there is this graph now it
appears to show the fraction of skin
particles in Airborne dust as 80 percent
except not really this is a stacked area
graph so dead skin accounts for only 20
percent of dust particles between 100
and 300 micrometers could a simple
misunderstanding of this graph be the
source of the urban legend I mean it's
possible but what's more interesting to
me is that the legend is not that far
off according to this a full 50 percent
of dust particles under 100 micrometers
is dead human skin the book also reports
on a study where they vacuumed a
mattress and studied the resulting dust
ball under the microscope 53 percent of
the Dust was skin particles
so the debunkers are debunked while not
70 to 80 percent dead skin cells do make
up a significant portion of household
dust of course the exact percentage
depends a lot on how much other dust is
contributed by the environment these
studies were conducted in houses in the
Netherlands which typically have
hardwood floors and therefore less dust
than homes with carpeting
it also depends on how large of a
particle you consider dust dead skin
cells account for roughly half of these
small dust particles but much less than
half of what is sucked up by your vacuum
cleaner
oh that is gross unbelievable
I guess it makes sense that the place
where we find the most dead skin cells
is in and around our beds where we spend
a third of Our Lives shedding a third of
our skin in our sleep
so then is it true that your mattress
actually doubles in weight every 10
years this claim was actually published
in a major news Outlet 20 years ago with
the increase in Mass attributed to dust
mites that feed on your dead skin the
claim which lacked a scientific
reference is so disgusting it has spread
throughout the internet but it's not
true if two people slept on the same bed
for a decade and even if all their dead
skin cells ended up in the mattress it
would only gain around three kilograms
or seven pounds and by conservation of
mass the dust mites that feed off that
dead skin could not weigh more than that
so the total weight gain would have to
be less than 10 percent the weight of an
average mattress and remember dead skin
cells are small and light enough to
become airborne just making the bed has
been found to increase the number of
skin flakes in a cubic meter of air from
000 to a hundred and seven thousand
skin scale dust is inevitable and it
occurs in higher quantities where there
are more people scientists have studied
the Airborne dust in the London
Underground and found that fragments of
dead skin cells make up around 10
percent of all small dust particles by
weight
and it's not just skin we are shedding a
ton of tiny organisms live on our bodies
a teeming microbiome of bacteria fungi
and mites every hour we shed
approximately 1 million microbes in a
cloud that spreads out a radius of about
one meter from our bodies in one study
an individual was placed in a clean room
for 90 minutes scientists then
identified who had been in the room not
using their DNA but rather using the
characteristic fingerprint of their
microbial Cloud the technique was so
accurate the team wrote that it clearly
suggests a forensic application for
indoor bio aerosols I mean that one day
we will likely use microbial dust clouds
to solve crimes
dust can reveal a lot about us because a
significant fraction of it literally is
us I mean everyone has heard the
expression dust to dust but they're
probably not thinking about how each and
every day part of us is becoming dust
you know when I was reading this house
dust Biology book I found some sections
that sounded to me a little bit like
poetry so studying dust from an office
under a light microscope revealed tree
fibers from paper eraser dust rubber
calcite and pumice human hair various
dyed wools Cottons and synthetic fibers
such as nylon rayon cellulose triacetate
and Orlon dander tobacco cigarette ashes
graphite wood shavings oil soot paint
chips glue fingernail filings and traces
of quartz and starch I love all these
words because they bring Vivid images to
mind it's like the tiniest fragments of
Our Lives can paint a full picture of
reality of who is there and what they
did
you know searching through dust is a
little like searching the internet there
are so many pieces it's fuzzy nebulous
but with the right tools and a bit of
perseverance I'm confident that we can
uncover the truth buried in there in
this case the truth is that dust
particularly these small particles and
dust around beds is mostly dead skin
why does that matter
because it is something we can be
certain about I mean for centuries
science has beaten back the shrouds of
ignorance and knowing what is really
true is the only way we have been able
to make progress
the internet gives us a great
opportunity to share that knowledge but
only if someone takes the time to
research and establish what really is
true
to perform a lot of This research I have
of course been using Google which might
make you wonder how they figure out what
to show you in the first place well good
news Google is not a black box they have
an entire website that takes you under
the hood of the search engine and
explains all the testing and
improvements they make check it out by
clicking the link in the description and
when you go to make your next search Try
it a few different ways start broad
don't include your answer in the query
use image search and most importantly
remember Google shows you the most
relevant information it's up to you to
decide what to do with it
thanks to Google for sponsoring this
video learn more about search by
clicking the link in the description