How Dirty Is Soap?

It’s good hygiene to wash your hands after touching shared bathroom surfaces. But bars of soap are a shared surface. Does soap really help get you clean?

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
it's Christian Seger. It's good hygiene to wash your hands
after using the restroom and after touching kind of gross stuff,
you know, like raw meat, snakes, cat litter, cats, biomedical waste,

(00:22):
and any number of shared surfaces from door knobs to countertops.
But what about soap? Bars of soap are also shared surfaces.
So how dirty is soap? Soap is absolutely seething with bacteria,
But you know, so is your face, and so so
is my face and everything we come into contact with

(00:42):
all day, every day. Really, organism for organism, microbes outnumber
humans on the planet at least a hundred and thirty
one quintillion to one. Sell for sell, The microbes in
and on our bodies outnumber us ten to one, and
human hands can have up to one hundred thousand micro
organisms per square centimeter of skin. Most of them are

(01:06):
harmless or you know, even helpful, but yeah, there's a
lot of them, and some of them get transferred to
your soap. One study from reported that of the bar
soaps they tested, two tocent cultured positive for micro organisms.
The antibacterial soap they tested actually had a bit more

(01:28):
microbial activity than regular soap. The soaps in question were
in use by the staff of clinics and laboratories over
the course of seven days, and samples were taken on
five of those days. But the interesting and comforting part
of their results is that the microbes didn't build over
the course of that week. Organisms would appear and disappear

(01:50):
with each sample taken, indicating one of two things. Either
the soaps were somehow self sterilizing, possibly due to preservatives
they can tane that are you know, not delicious or
downright dastardly to microbes, or the little buggers were being
mechanically removed during the process of washing, meaning that as

(02:11):
you wash your hands, you're also washing your soap. These
results back up a couple of other studies about microbes
and hand washing, one from ninety and one from The
former study had subjects come into their lab, douse a
hand in a vat of bacteria, and then wash with
a bar of soap. The soap was tested for the bacteria,

(02:32):
then given to another subject to assess the transfer of
the bacteria. The latter study carefully doused bars of soap
with ecle i and had subjects come in and first
sterilized their hands, then wash them with this gross soap.
The researchers then tested both the hands and the soap
for microbes. Both of these studies found that although bacteria

(02:55):
remained on the soaps, none transferred to the participants hands.
Now here's the thing to note. These studies were done
by employees of Procter and Gamble and Dial Corporation, respectively,
and the first study I mentioned that one from that
was completed with a grant from Minnatonka Incorporated, which was
the original maker of soft soap. That doesn't necessarily mean

(03:18):
their science was bad, though experts say there's no evidence
to contradict their results. So bar soap is not underty,
but it's still safe to use and way better than
not washing. So here's a few pro tips. Be sure
to dry your hands thoroughly after washing. Don't wash more
often than necessary. That can lead to parched skin, which

(03:42):
can crack, which can let in microbes. You otherwise would
have been able to just wash off. And make sure
you store bar soap in a dish that lets it
drain and dry out between uses. That'll cut down on
any potential bacterial growth. Check out the brainstuff channel on YouTube,

(04:05):
and for more on this and thousands of other topics,
visit how stuff Works dot com.