Image: Washing hands
Getty Images file
Another reason to wash up: Both men and women have more types of bacteria on their hands than researchers expected to find.
updated 11/3/2008 5:00:27 PM ET 2008-11-03T22:00:27

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.

The perils of hand-holding
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.

  1. Don't miss these Health stories
    1. Splash News
      More women opting for preventive mastectomy - but should they be?

      Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

    2. Larry Page's damaged vocal cords: Treatment comes with trade-offs
    3. Report questioning salt guidelines riles heart experts
    4. CDC: 2012 was deadliest year for West Nile in US
    5. What stresses moms most? Themselves, survey says

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 also 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.

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Discuss:

Discussion comments

,

Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments