You may have heard about a study saying women’s hands have more types of bacteria than guys. But, as you’ll see in this ScienCentral video, that study shows other fascinating things: bacteria on your right hand differ from your left and, while hand-washing is effective in combating bacteria, bacteria levels come back quickly.
Hands hold more than you think
Did you ever wonder how well hand washing works? A study led by the University of Colorado’s Noah Fierer is giving us all a good sense of what is living on the palms of our hands.
Using DNA sequencing to identify the types of bacterial communities living on people’s hands, Fierer says the researchers found that, “the average palm surface has about 150 species of bacteria.”
Good Bacteria/Bad Bacteria
For those whose palms get sweaty at the idea, Fierer offers some reassurance, noting, bacteria are all over your body and, “that’s nothing to be feared.” He agrees there are bad bacteria, but points out that a lot are not bad, adding, “In fact, they may protect you from getting diseases.”
While it is well known your body has bacteria– by some estimates 10 bacteria for every cell in your body– until recently it was not possible to identify those bacteria. Even to scientists looking through powerful microscopes, bacteria are hard to identify. The only certain way is through their DNA, and only recently has it been possible to sequence DNA quickly enough to be useful in studying bacteria.
Men Versus Women
In one study, published in the Proceedings of the National Academy of Sciences in 2008, the researchers studied 51 graduate students.
The study showed a person typically has different bacteria on their right and left hands. Notes Fierer, “On average, only 17 percent of the communities on your left hand are shared by your right hand.”
The researchers also discuss how men and women’s hands differ, noting, “the palms of women were… found to harbor significantly greater bacterial diversity than those of men.”
Fierer jokes about the results, saying, “Essentially, we answered the age-old question, ‘Do girls have cooties?’” He adds, Girls are unlikely to have more cooties, i.e. bacteria, than men, but they have more types of bacteria”. In the report they speculate that the greater diversity of bacteria communities is the result of a natural difference in the acidity of men and women’s skin.
Why study hands? Fierer, whose usual source of research is bacteria and fungus in places like soil and on leaves, says this study was prompted by “pure curiosity.” However, he says once they saw the results they realized that, “the research has a lot of very applied implications.” He points out that for example, “If we want to know which communities make somebody more prone to getting a disease, we first need to know the background variability within a population.”
They also studied in detail the impact of hand washing. It’s well known that washing your hands helps stop bacteria and disease, but this study took a more in-depth view of the issue. Fierer says, “We found between two and four hours after hand washing, the community was back to quote/unquote normal.” He says that makes sense, because, “if you’re a bacteria that can’t survive hand washing you’re not going to stay on the hand very long.”
They also found out that your hand bacteria don’t change all that much as you go about touching things. He says it, “It suggests that each person has their own unique bacterial signature” but adds that additional study will be needed to see if that stays true over long periods or from season to season.
This research was published online November 3, 2008 in the Proceedings of the National Academy of Sciences and was funded through a grant from the National Institutes of Health.
Elsewhere on the Web:
The Human Microbiome Project
The Bacterial Flora of Humans