Close Look at Human Arm Finds Host of Diverse Species

Hold out your hand, with the palm facing skyward. Pull the sleeve of your shirt up to your elbow. Now take a look at the fleshy part of your arm, about halfway between your wrist and your elbow. What do you see?

Nothing, probably.

But that's not what Martin J. Blaser of New York University School of Medicine sees. With the help of the latest scientific tools, Blaser sees a complex, microscopic world teeming with a vast array of microorganisms.

"The skin is home to a virtual zoo," said Blaser, a microbiologist who last week published online the first molecular analysis of the bacteria living on one small patch of human skin. "We're just beginning to explore it."

The analysis revealed that human skin is populated by a diverse assortment of bacteria, including many previously unknown species, offering the first detailed peek at this potentially crucial ecosystem.

The work is part of a broader effort by a small coterie of scientists to better understand the microbial world that populates the human body. Virtually every orifice and the digestive tract are swarming with bacteria, fungi and other microbes. By some estimates, only one out of every 10 cells in the body is human.

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Scientists suspect these microbes play important but poorly understood roles, assisting crucial bodily functions and potentially helping prevent or cause many diseases. One recent study found that obese people appear to have a unique mix of microbes in their guts, which could partly account for the obesity epidemic.

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"The result of this human microbiome project will be a more comprehensive view of our genetic landscape and should provide insights about which of our 'human attributes' are derived from products of our microbial self," he said. "This could lead, in turn, to new ways of defining health, new ways for predicting disease predilection, and new ways for treating illnesses affecting various components of our body, including the skin."

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Blaser's team swabbed an area of skin about the size of silver dollar on the right and left forearms of three healthy men and three healthy women. They then used sophisticated molecular techniques to amplify and analyze fragments of bacterial DNA captured by the swabs.

The analysis revealed 182 species, the researchers reported. Of those, 30 had never been seen. They identified an additional 65 species when they sampled four of the volunteers eight to 10 months later, including 14 new species.

"We found a lot of diversity -- both in terms of distant relatives but also cousins. And not just first cousins, but second, third and fourth cousins," Blaser said.

On average, each person's skin harbored about 50 species, but only four of them were found on all six people, suggesting that the mix of bacteria varies significantly from person to person. But those four species accounted for more than half of all the DNA sequences found, indicating that a relatively few species tend to dominate. And when the researchers analyzed the bacteria using a broader classification, phylum, they found three phyla on all six subjects that accounted for 95 percent of all present species.

"It appears that there is a conserved infrastructure or scaffolding of organisms that's common in human skin, and then a lot of transient or uncommon organisms that are person-specific," Blaser said.

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In fact, when the researchers sampled four of the six volunteers a second time, they found many of the species detected earlier were gone.

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Scientists assume that most of the organisms have a symbiotic relationship with their human hosts and play some type of beneficial role. But the next step will be to try to characterize their functions.

"We're interested in understanding how we interact with these organisms and how they are communicating with human cells and vice versa," Blaser said.

Some of the organisms may also play a role in diseases such as eczema and psoriasis.

"These are chronic inflammatory diseases of the skin of unknown cause. If these microorganisms have something to do with skin disease, knowing what's there may help us diagnose or perhaps treat these diseases," he said.

Blaser noted that human skin probably has myriad distinct ecosystems, noting that a similar study looking at fungi produced similar results but also found tremendous diversity in different parts of the body.

Emphasis mine. Since I generally swim 5 days a week, am I washing away beneficial ecosystems? Or some of my "human attributes"? Then there's this:

Pheromones are chemicals emitted by living organisms in order to sexually attract a member of the opposite sex of the same species. Female insects, for example, excrete pheromones that will attract male insects up to 10 kilometres away.

[Ariel Fenster, a chemistry professor at McGill University] said there is evidence to suggest a physical response to being in love, although there are no definitive answers.

Studies have been done observing the mating habits of pigs, where the male pig will release pheromones to attract a female pig when ready to mate.

“What is interesting is that male pig pheromones are present in men,” Fenster said.

These sexual agents known as pheromones, more specifically, androstenol, are subtly emitted through a man’s sweat and are also carried by women. Whether or not they are effective in wooing members of the opposite sex is still unknown..

And this:

Male sweat contains a compound that appears to boost women's mood, sexual arousal, and stress hormone levels.

So says Claire Wyart, Ph.D., a postdoctoral fellow at the University of California, Berkeley Olfactory Research Project, and colleagues.

The compound, called androstadienone (AND), "does cause hormonal, as well as physiological and psychological, changes in women," Wyart says in a university news release.

So what else am I washing away? Maybe I shouldn't bathe at all.

Save the ecosystem! Save your love life! Don't bathe!