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Women have a greater range of different types of bacteria on the palms of their
hands than men, US research suggests.
The study also found that human hands harbour far higher numbers of bacteria
species than previously thought.
Using powerful gene sequencing techniques, researchers found a typical hand had
roughly 150 different species of bacteria living on it.
The Proceedings of the National Academy of Sciences study found bacteria types
varied greatly between individuals.
The sheer number of bacteria species detected on the hands of the study
participants was a big surprise
Dr Noah Fierer
Universithy of Colorado at Boulder
The researchers, from the University of Colorado at Boulder, hope their work
will help scientists to establish a "healthy baseline" of bacteria species on
the human hand.
This could potentially help them to identify which species are linked to
specific diseases.
Lead researcher Dr Noah Fierer said: "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."
The study detected and identified more than 4,700 different bacteria species
across 102 human hands in the study.
However, only five species were shared among all 51 participants.
Even the right and left palms of the same individual shared an average of only
17% of the same bacteria types.
Acidic skin
Dr Fierer said that the higher bacterial diversity on women's hands may be due
to the fact that men tend to have more acidic skin, which provides a more harsh
living environment for the microscopic bugs.
Alternatively, differences in sweat, oil gland or hormone production may be key
- or the fact that women and men tend to make different use of cosmetics such
as moisturisers.
Dr Fierer said the study also found hand washing had little impact on the
diversity of bacteria found on an individual's hands.
While some groups of bacteria were less abundant following hand washing, others
were more abundant.
However, the researchers said that washing with anti-bacterial cleansers was
still an effective way to minimise the risk of disease, as it seemed
particularly to target harmful bugs.
The diversity of bacteria types on the palm was three times higher than that
found on the forearm and elbow and appeared to outstrip that found in the mouth
and lower intestine.
Important role
Dr Fierer said: "We know that skin associated bacteria are likely to have an
important influence on skin health, a minority may act as pathogens and many
may actually have a beneficial effect, protecting us from disease.
"However, we do not know how differences in bacterial communities may impact
skin health and we do not know if specific types of bacteria are more
beneficial than others.
"This is an active area of research but our results suggest that answering
these questions will be very difficult given that there is so much background
variability in bacterial communities between healthy individuals."
Dr Valerie Curtis, director of the Hygiene Centre at the London School of
Hygiene and Tropical Medicine, said science still had much to learn about how
bacteria interact with the human body.
She said: "Most are likely to be neutral, just living there without doing any
harm or good."
But she added: "It is thought that having such flora on our hands is probably
beneficial, because the bacteria occupy niches which are then unavailable to
pathogens."