November 4, 2008

Bacteria Thrive On Female Hands

Are women actually the dirtier of the two sexes?

The answer is yes, according to a new study that found ladies have a greater variety of bacteria on their hands compared to men.

"One thing that really is astonishing is the variability between individuals, and also between hands on the same individual," said co-author and University of Colorado biochemistry assistant professor Rob Knight.

"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," added lead researcher Noah Fierer, an assistant professor in Colorado's department of ecology and evolutionary biology.

The research team believes women have more bacteria because they have less acidic skin than men.

Fierer said differences in sweat and oil gland production between men and women, the frequency of moisturizer or cosmetics applications, skin thickness or hormone production set the sexes apart. 

Knight stressed that "the vast majority of the bacteria we have on our body are either harmless or beneficial ... the pathogens are a small minority."

In the study, researchers gathered samples from the palms of 51 college students, a total of 102 hands. They then tested the samples using a new, highly detailed system for detecting bacterial DNA.

They found 4,742 species of bacteria, they reported on Monday's online edition of Proceedings of the National Academy of Sciences.

The study noted the average hand harbored 150 species of bacteria.

Researchers also said the left and right hands of the same individual shared only about 17 percent of the same bacteria types.

Fierer said differences between dominant and non-dominant hands were due to environmental conditions like oil production, salinity, moisture, or variable surfaces touched by either hand of an individual.

Researchers said hand washing was important for good health, but noted that washing did not eliminate bacteria.

"Either the bacterial colonies rapidly re-establish after hand washing, or washing (as practiced by the students included in this study) does not remove the majority of bacteria taxa found on the skin surface," the researchers said in their report.
The tests found how many different types of bacteria were present but could not count the total amount of bacteria on each hand.

The National Institutes of Health and the National Science Foundation paid for the study.

Knight said the researchers hope to repeat the experiment in other countries where different hands are assigned specific tasks.


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