By RANDOLPH E. SCHMID,AP Science Writer AP -
Tuesday, November 4
WASHINGTON - Wash your hands, folks, especially you
ladies. A new study found that women have a greater variety of
bacteria on their hands than men do. And everybody has more types
of bacteria than the researchers expected to find.
"One thing that really is astonishing is the variability between
individuals, and also between hands on the same individual," said
University of Colorado biochemistry assistant professor Rob Knight,
a co-author of the paper.
"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 researchers aren't sure why women harbored a greater variety
of bacteria than men, but Fierer suggested it may have to so with
the acidity of the skin. Knight said men generally have more acidic
skin than women.
Other possibilities are differences in sweat and oil gland
production between men and women, the frequency of moisturizer or
cosmetics applications, skin thickness or hormone production, he
said.
Women also may have more bacteria living under the surface of
the skin where they are not accessible to washing, Knight
added.
Asked if guys should worry about holding hands with girls,
Knight said: "I guess it depends on which girl."
He stressed that "the vast majority of the bacteria we have on
our body are either harmless or beneficial ... the pathogens are a
small minority."
The researchers took samples from the palms of 51 college
students _ that's 102 hands _ and tested the samples using a new,
highly detailed system for detecting bacteria DNA.
They identified 4,742 species of bacteria overall, only 5 of
which were on every hand, they report on Monday's online edition of
Proceedings of the National Academy of Sciences.
The average hand harbored 150 species of bacteria.
Not only did individuals have few types of bacteria in common,
the left and right hands of the same individual shared only about
17 percent of the same bacteria types, the researchers found.
The differences between dominant and non-dominant hands were
probably due to environmental conditions like oil production,
salinity, moisture or variable environmental surfaces touched by
either hand of an individual, Fierer said.
Knight said the researchers hope to repeat the experiment in
other countries where different hands are assigned specific
tasks.
While the researchers stressed the importance of regular hand
washing, they also 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.
While the tests could determine how many different types of
bacteria were present, they could not count the total amount of
bacteria on each hand.
The research was funded primarily by the National Institutes of
Health and the National Science Foundation.