The Learning Blog

Last November 2008, a University of Colorado study entitled “The influence of sex, handedness, and washing on the diversity of hand surface bacteria” was presented to the National Academy of Sciences. The lead author of the study is Asst Prof Noah Fierer of the university’s Ecology and Evolutionary Biology Department.

The study’s abstract stated:

Bacteria thrive on and within the human body. One of the largest human-associated microbial habitats is the skin surface, which harbors large numbers of bacteria that can have important effects on health. We examined the palmar surfaces of the dominant and nondominant hands of 51 healthy young adult volunteers to characterize bacterial diversity on hands and to assess its variability within and between individuals. We used a novel pyrosequencing-based method that allowed us to survey hand surface bacterial communities at an unprecedented level of detail. The diversity of skin-associated bacterial communities was surprisingly high; a typical hand surface harbored >150 unique species-level bacterial phylotypes, and we identified a total of 4,742 unique phylotypes across all of the hands examined. Although there was a core set of bacterial taxa commonly found on the palm surface, we observed pronounced intra- and interpersonal variation in bacterial community composition: hands from the same individual shared only 17% of their phylotypes, with different individuals sharing only 13%. Women had significantly higher diversity than men, and community composition was significantly affected by handedness, time since last hand washing, and an individual’s sex. The variation within and between individuals in microbial ecology illustrated by this study emphasizes the challenges inherent in defining what constitutes a ‘‘healthy’’ bacterial community; addressing these challenges will be critical for the International Human Microbiome Project.

In other words…

• The study found 150 different bacterial species in a typical hand. It also found a total 4742 different bacterial species from all the subjects.
• For an individual, both hands only share 17% of the bacteria found.
• Between different people, only 13% of bacteria were found common.
• That women have more bacterial diversity than men. The explanation is yet unknown but it is suggested that the pH may have an influence to this finding. It is known that men have more acidic skin than women.

In addition:

• Between dominant and nondominant hands, although the diversity of both are equal, their composition was different. This difference is likely due to different skin conditions like sebum production, salinity, and hydration or that the dominant hand has more contact to environmental surfaces than the nondominant hand.
• That the composition (but not the levels) of bacteria is dependent on the frequency of handwashing. Thus, the authors have considered hand-washing with an anti-bacterial soap as having a “positive effect”.
• There are about 3x more bacteria on the palm of our hands as compared to the elbow or forearm.
• A video about this study can be viewed here.

Clinically, we only need to advise patients — more on female patients than male — to properly wash their hands frequently so as to reduce transmission of bacteria and other infectious agents.

Click image to enlarge.

For the study’s complete report, click here.

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

1. » Study: Skin bacteria on sex, handedness, and handwashing Raphael’s Friendster Blog says:

   12/28/2008 at 00:08

   [...] here for [...]
2. workstation risk assessment says:

   12/29/2008 at 04:45

   workstation risk assessment…

   safety newsletters…
3. Sharon McEachern says:

   01/22/2009 at 03:47

   Hello Raphael — This is to let you know that your post on hand washing inspired me and I just wrote a post of my own on Ethic Soup about physicians not washing their hands, along with the desperate attempts of hospitals to get them to wash. They’re trying everything from threatening a loss of hospital priviledges and termination to monitoring soap supplies, using hospital staff as “spies” and even covert cameras! Hospitals in Houston, TX give laminated print-outs for patients with their first hospital meal, urging them to ask their doctors to wash the hands before examinations.

   Thanks for the inspiration! My article is at:

   http://www.ethicsoup.com/2009/01/dont-kill-me-doctor-wash-your-hands.html

   Sharon