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Interactive video lesson plan for: How Dirty Is Soap?

Activity overview:

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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It’s good hygiene to wash your hands after using the restroom, and after touching kinda gross stuff like raw meat, snakes, cat litter, cats, biomedical waste, and any number of shared surfaces from doorknobs to countertops. But what about soap? Bars of soap are also shared surfaces. So how dirty is soap?

Organism for organism, microbes outnumber humans on the planet at least 131-quintillion-to-one. Cell for cell, the microbes in and on our bodies outnumber us ten-to-one.

And human hands can have up to 100,000 microorganisms per square centimeter of skin. Most of ‘em are harmless or even helpful, but yeah, there’s a lot of them. And some of them get transferred to your soap.

One study from 1984 reported that of the bar soaps they tested, 92-to-96% cultured positive for microorganisms. The antibacterial soap they tested actually had a bit more microbial activity than the regular soap.

The soaps in question were in use by the staff of clinics and laboratories over the course of 7 days, and samples were taken on 5 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 with each sample taken, indicating one of two things.

Either the soaps were somehow self-sterilizing, possibly due to preservatives they contain that are un-delicious or downright dastardly to microbes.

Or the little 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 handwashing, one from 1965 and one from 1988. Both of these studies found that although bacteria remained on the soaps, none transferred to the participants’ hands.

Now, a thing to note: These studies were done by employees of Proctor & Gamble and Dial Corporation, respectively. And the first study I mentioned, from ’84? Was completed with a grant from Minnetonka, Inc., which was the original maker of Softsoap. That doesn’t necessarily mean their sciences were bad, though. Experts say there’s no evidence to contradict their results.

So bar soap is not un-dirty, but still safe to use, and way better than not washing.

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 can crack, which can let in microbes you otherwise would’ve 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.


Tagged under: brainstuff,brain stuff,howstuffworks, stuff works,science,technology,lauren vogelbaum,techstuff,fw thinking,soap,wash,washing,bacteria,fungus,disease,microbes,microorganisms,hands,restrooms,bathrooms,bacterial, dirty soap,handwashing,washing hands,antibacterial,hand soap

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