14 January 2013

Follow up: Is bar soap dirty?

In August 2012, I asked:
Why does everyone use liquid soap? [...] Is liquid soap more sanitary? I found one secondary source that says "[g]erms can grow on bar soap." But wouldn't viruses, molds, and bacteria just wash off your hands with the mechanical action of washing and rinsing, and the chemical action of soap micelles forming around them? And what bacteria can grow on bar soap, anyway? I thought one of the basic (ha-ha) things about soap was that it lyses bacteria when the business end of a hydrophobic-hydophilic soap molecule disrupts a bacterium's lipid membrane. There must be more types of bacteria in heaven and earth, Horatio, than are dreamt of in my philosophy.
(Internal links omitted. Pretentious reference to Shakespeare retained.)

Well! Following some bouncing links the other day, I found an answer. Some of the links in the article no longer work, but here we go:
According to a series of tests conducted in the early 1980s, bars of soap are often covered with bacteria and carry a higher load than you'd find inside a liquid dispenser. But no one knows for sure whether this dirty soap will actually transfer its germs to your hands during a wash.

In fact, what little clinical evidence there is suggests that dirty soap isn't so bad. A study from 1965 and another from 1988 used similar methodologies: Researchers coated bars of soap in the lab with E. coli and other nasty bacteria, and then gave them to test subjects for a vigorous hand-wash. Both teams found no transfer of contamination from the dirty soap. However, both studies were tainted by potential conflicts of interest: The first was conducted by Procter & Gamble, and the second came from the Dial Corp.

Still, there's no good evidence to contradict these studies, and it's likely that the bacteria on a dirty bar would just wash off when you rinsed your hands. In other words, you'd be cleaning the soap as you cleaned your hands.
I always understood that it doesn't matter what texture of soap you use, because any soap works in two ways, due to its chemical makeup. First, the soap molecule disrupts a bacterium's cell membrane. Two, the friction of rubbing your hands together, plus the slipperiness of the basic (as opposed to acidic) soap solution you create by lathering up, plus the rinsing action of water, all work together to mechanically remove dirt, bacteria, and viruses from your skin. The Mayo Clinic agrees, telling us essentially, just wash yer dang hands, and it doesn't matter if you use liquid, bar or powder soap.

Does anybody else remember using powdered soap? An elementary school of mine, built in 1929 with bathrooms likely dating to the post-Second World War era when I attended, featured powdered soap dispensers. I didn't figure anybody really used it any more, but Google text and image searches show current vendors and new dispensers.

But my take-away from all this is that I'm going to stick with my bar soap. And, now that the continental U.S. is enduring an extreme flu season this year, I'm going to wash my hands super frequently. The math lies squarely in favor of bar soap versus liquid soap. And I don't see a reason to install dispensers ($35.00 each) for powdered soap ($11.25 per 5-lb. box) in my home.

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