Human skin is a "virtual zoo" of bacteria, say researchers who have identified more than 200 species in samples taken from the forearm.
Staphylococcus bacteria are commonly found on the skin
About 8% of the species were previously unknown, according to the study published online in Proceedings of the National Academy of Sciences.
The team at New York Medical School used genetic analysis to work out what bacteria were present.
Microbiology experts said bacteria had a vital role in keeping skin healthy.
In the past our knowledge of bacteria has come from observing what happened when cells were grown in culture in a Petri dish.
But researchers now have much more sensitive techniques at their fingertips.
Recent work has looked at what bacteria are present in areas such as the gut and the mouth.
Study leader Professor Martin Blaser, professor of microbiology, and colleagues extracted ribosomal DNA from bacteria found in skin samples taken from forearms of six volunteers.
They amplified the rDNA and used markers to pick out genetic regions specific to different species of bacteria.
Participants were swabbed again eight to 10 months later to see if there had been any changes.
In the first set of analysis, the team found 182 species of bacteria, but at the repeated test a further 65 showed up.
Just over half of the bacteria found in the skin samples belonged to species that were already known to be common - Propionibacteria, Corynebacteria, Staphylococcus and Streptococcus.
And 8% were species that had not previously been described in the literature.
Almost three-quarters of the total number of bacterial species were unique to individual volunteers, suggesting the skin is "highly diversified".
Professor Blaser said: "Over the years maybe about 50 different organisms have been found in human skin but we knew there were organisms present that we couldn't grow. "We have gone up five-fold from what's been known before."
He now plans to repeat the study in people who have certain skin conditions such as psoriasis or eczema.
"The skin is home to a virtual zoo of bacteria. I see this as a form of explanation to see what's there."
Dr Richard Bojar, principal research fellow at the skin research centre, said there had been an explosion in the number of different bacteria identified because of better technology, but it did not necessarily have a clinical application.
"We have now got such a broad range of organisms. But these studies can't tell you how much are there.
"We now need to look at how we can use the technology usefully."
He added: "The microflora in your skin is important to keep your skin healthy but these days people tend to take more showers and use chemicals."
"The ancient Romans wiped on olive oil and wiped it off which gives you very good skin."