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Bacteria Abound on Hands

Hand Washing, Bacteria

Lady (“Out damned spot!”) Macbeth would have gone even more nuts had she learned the results of a recent study published in Proceedings of the National Academy of Sciences. According to the study, the average hand hosts 150 different species of bacteria — and women’s hands, apparently, teem with more varieties of bacteria than do men’s. The truly horrifying thing for Lady Macbeth would have been that washing her hands wouldn’t necessarily get rid of the little buggers.

The researchers recruited 51 undergraduates from the University of Colorado, giving them a total of 102 hands to study. They found 4,700 different types of bacteria on those hands, with only five species common to all subjects. Plus, it turns out the left hand really doesn’t know what the right hand is doing: individuals had completely different bacteria on their right and left hands, with only 17 percent of the species appearing on both hands.

Lead researcher Noah Fierer says, “The sheer number of bacteria species detected on the hands of the study participants was a big surprise and so was the greater diversity of bacteria we found on the hands of women.” That surprise came in part because this time the researchers used new, more sensitive technology to detect bacterial DNA than in the past. In fact, the results showed 100 times more bacteria gene sequences than those detected from earlier studies.

But why do women have more bacteria than men? Researchers speculate that it has something to do with skin pH, since men have more acidic skin than women. They also point to the fact that women use more cosmetics and perfumes, sweat less, have thinner skin and different hormonal secretions. They don’t mention the fact that even these days, women still tend to do the most typing and touch the most office equipment, change the most diapers, do the most laundry, spend the most time battling dirty dishes and cooking the bulk of bacteria-laden food. (A study earlier this year found that husbands add an average of seven extra hours of housework each week to their wife’s load.) Even so, most people would have assumed that men carry the greater burden of skin bacteria because men are Neanderthals by nature and women are more hygienic.

Well, perhaps women are more conscientious when it comes to washing up (though I haven’t seen any studies affirming this), but it doesn’t matter. It turns out that washing hands did not significantly reduce the number of bacteria present. Washing got rid of some types of bacteria, but other species actually became more plentiful after washing. The report in the Proceedings noted that, “Although hand washing altered “community” composition, overall levels of bacterial diversity were unrelated to the time since the last hand washing. Either the bacterial colonies rapidly re-establish after hand washing, or washing (as practiced by the students included in this study) did not remove the majority of bacteria taxa found on the skin surface.”

Still, researcher Rob Knight insists that regular washing with anti-microbial soap would help in promoting public health. Hmm! If washing does little to reduce the bacterial colonies happily living on your palms, that logic seems skewed– especially when you don’t know whether lathering up is killing the good bacteria on your hands or the evil microbes, since most bacteria, in fact, are not pathogenic and many are actually helpful. And what’s with the recommendation to use antibacterial soap?

As I’ve written before, existing research shows that antibacterial hand-soaps work no better than regular soap and water in minimizing germs or disease, and in fact, may promote the growth of antibiotic-resistant bacteria (though this is a hotly debated subject, with studies supporting both sides of the argument). (And this new study tells us that no kind of soap really does the job.) In addition, studies have revealed that ingredients found in 76 percent of antibacterial soaps — triclosan and triclocarban — may actually contribute to autism, enlarge the prostate, reduce fertility in women and men, bring on early puberty, and increase cancers of the breast, ovaries, and prostate, as well as hinder nervous system function. So why use antibacterial soaps — in spite of continued enthusiasm from the medical community?

It seems that we operate under several deeply ingrained delusions — the first, that women are more pristine than men, and the second, that washing more will wipe away the germs — and so we collectively spend more than a billion dollars annually on antibacterial products.

At the least, scientists do hope to use the results of this study to determine which bacteria are “normal” on the hands and which are problematic. “Today we have the ability to answer large-scale questions about these complex microbial communities and their implications for human health that we weren’t even asking six months or a year ago,” says Dr. Fierer. Sounds like a step in the right direction.

And as for Lady MacBeth…it’s a good thing she didn’t live in the 21st century. She most likely would have been confused by the dozens of conflicting studies, as well as too broke from buying countless antibacterial soaps to go through with her suicide — and that would have destroyed the plot of one of the world’s great plays.