If you're an innie and not an outie, your belly button is home to at least 60 to 100 or more species of bacteria, fungi and yeasts, according to new research.
The findings, to be presented on Aug. 12 at the Ecological Society of America's 96th Annual Meeting in Austin, Texas, demonstrate how a belly button can become a haven for complex biodiversity.
"Although we find about 60 or 70 species on the average person, we have found more than 1400 species overall, such that differences among individuals are great," Rob Dunn, assistant professor in the Department of Biology at North Carolina State University, told Discovery News.
Dunn and his colleagues have so far collected skin bacteria from the belly buttons of 391 test subjects from across the nation. Men and women of different ages and ethic backgrounds, and even differing hygienic habits, were included in the study. The researchers have been focusing on bacterial content within the samples, but "there are also fungi and some interesting yeasts," Dunn said.
The scientists have confirmed the viability of these organisms by culturing, and are now in the process of sequencing each species' DNA.
Preliminary results indicate that the number of organisms per person highly varies, with each individual carrying his or her own unique mix.
"So far, we don't see clear explanations for why people differ so much in terms of their bacterial communities from person to person," Dunn said. "The differences we see don't match up easily with gender, ethnicity, age or even washing frequency. Something else is going on."
The researchers have, however, concluded that a group of relatively few bacterial species are shared among most of us, with hundreds of other rare species occurring here and there.
"It may be that we mostly share our common species, but that the rare species we encounter are a measure of our individual stories and are inherently unpredictable," he said.
The researchers chose to look at belly buttons, in part, because they tend to harbor so many organisms that are often undisturbed by cleansers, lotions, ultraviolet light and other things.
While many people might now be more mindful of belly button washing, Dunn said such organisms that are also found on our forearms, hands and really the entire surface of the body, serve an important function.
"They are a kind of first line defense against pathogens that land on us, a kind of living army on our skin that when it meets a newly arriving pathogen has, as a first response, to try to compete," Dunn explained. "A human who successfully scrubbed all of the microbes off of his or her body would be at incredibly high risk of a deadly skin infection."
Various species also live inside of our bodies, especially in the gut, which he describes as being "a kind of living wonderland of single-celled life."
In a paper accepted for publication in the journal Animal Behaviour, Elizabeth Archie of the University of Notre Dame and colleague Kevin Theis analyze microbial communities on humans and other animals. They point out that the bacteria may even change the behavior of its hosts. Steroids and other natural chemicals found under human armpits are one example. These compounds are primarily products of bacterial metabolism, and can result in all sorts of funky odors that affect how we interact with each other.
"For instance, some Corynebacterium metabolize testosterone to produce a musky, urine-like scent, while others metabolize sebum and sweat to produce an onion-like odor," Archie and Theis write. "There is ample evidence that bacteria produce strong axillary odor, and that armpit odors serve as recognition cues among humans."
These cues, in turn, seem to help us to distinguish between individuals. Mothers, for example, have no trouble recognizing their children from their armpit smells alone.
Even with such family ties, our closest relationships in life are with the mysterious, ultra-tiny organisms.
"They are partners more intimate than our lovers, children, pets or any other organisms," Dunn said. "You are covered in unknown life. That life is doing things for or to you. Don't you feel like you should know about it?"