BrainStuff Classics: How Dirty Is Soap?

It’s good hygiene to wash your hands after touching shared bathroom surfaces. But bars of soap are also a shared surface. Learn why soap is pretty clean in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of I Heart Radio. Hey
brain Stuff. Lauren vog Obam here with a classic episode
from our erstwhile host, Christian Sagar. This is one that
I wrote in the way back for our YouTube series
because once the question occurred to me, I couldn't get
it out of my head. How dirty is soap? Hey

(00:26):
brain Stuff? It's Christian Sager. 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 waist 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

(00:51):
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 all the 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

(01:14):
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 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 to nine

(01:38):
percent cultured positive for micro organisms. The antibacterial soap they
tested actually had a bit more microbial activity than regular soap.
The soaps in question we're 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 come heating part of their results is

(02:01):
that the microbes didn't build over the course of that week.
Organisms would appear and disappear with each sample taken, indicating
one of two things. Either the soaps were somehow self sterilizing,
possibly due to preservatives they contain that are you know,
not delicious or downright dastardly to microbes, or the little

(02:23):
buggers were being mechanically removed during the process of washing,
meaning that as 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 x and
one from the former study had subjects come into their
lab douse a hand in a vat of bacteria and

(02:45):
then wash with a bar of soap. The soap was
tested for the bacteria, then given to another subject to
assess the transfer of the bacteria. The latter study carefully
doused bars of soap with ec. Cole I and had
subjects come in and first sterilize their hands, then wash
them with this gross soap. The researchers then tested both

(03:07):
the hands and the soap from microbes. Both of these
studies found that although bacteria remained on the soaps, none
transferred to the participant's 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

(03:29):
Minnatonka Incorporated, which was the original maker of soft soap.
That doesn't necessarily mean 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

(03:49):
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 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

(04:11):
will cut down on any potential bacterial growth. Today's episode
was written by me and produced by Tyler Clang. Brain
Stuff is production of iHeart Radio's How Stuff Works. For
more in this and lots of other clean topics, visit
our home planet, how stuff Works dot com. Plus for
more podcasts. For my heart Radio, visit the heart Radio app,

(04:32):
Apple Podcasts, or wherever you listen to your favorite shows,