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Human Skin Rich Ecosystem of Bacteria

Skin is our first line of defense against disease and injury. It's an essential barrier against the germs of the outside world. And when you look at your skin, it's hard to imagine that it's completely covered in bacteria. Now some new research finds your skin is even more colonized by micro-organisms than previously thought.

Despite bacteria's bad reputation, not all micro-organisms are bad, says Elizabeth Grice, a geneticist working at the U.S. National Human Genome Research Institute.

Grice says many bacteria play some kind of beneficial role in maintaining health. Others exacerbate skin diseases such as eczema or acne. But our knowledge about these microscopic hitchhikers is incomplete.

Grice and her colleagues decided to use some new technology to examine skin bacteria. They recruited 10 volunteers to donate samples of their skin bacteria, and the volunteers had skin scrapings taken from 20 different locations on their bodies.

"These areas were chosen based on the diversity in terms of the types of environments they are," Grice says. "For example, we chose a very hairy area of the body, the back of the scalp, but we also chose hairless areas such as the palm of the hand."

Grice used a genetic technique called PCR, or polymerase chain reaction testing, to examine the bacteria's DNA. This helped her identify the different micro-organisms more precisely. Previously, scientists were only able to identify bacteria that tolerated the growth media well. But with PCR testing, Grices says they were able to find bacterial species heretofore unknown on skin. And she says they found many more types than expected.

"The dominant bacteria in the oily areas is a propioni bacterium which we know is present in oily areas for the most part because this type of bacteria is able to break down the oils in our skin," Grice says. "In the moist areas, we commonly see Staphylococcus species, and in the drier areas, we generally see a greater mix and variety of bacteria. There didn't seem to be one dominant type."

Grice says surprisingly, dry areas of the skin, such as the forearm, had the greatest number and variety of bacterial species.

"Some of the drier areas are more exposed to the environment, and what we may have sampled from the drier areas may actually be transient bacteria and not actually bacteria that set up permanent residence there," she says.

Grice says there's much more to be learned about the many different kinds of bacteria on the skin and what role they play in health. And she posits that the bacterial environment on your skin may determine what types of pathogens you are susceptible to.

Grice's paper is published in the journal Science.