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Plunging into the Unknown: Belly Button Bacteria and You

Have you ever looked up at the night sky and wondered what kinds of life might exist out there? Well, you can look down – at your belly button that is – and wonder the exact same thing.

According to research published today in PLOS ONE, the belly button is home to an array of bacterial life ranging from the common (like Staphylococci) to the rare (like Archaea which have never been found before on human skin). Some bacteria, like those belonging to the Bacillus genus (pictured above), are feisty – they battle against fungi and viruses. Other bacteria, like those in the Micrococcus genus, are responsible for body odor!

All of this and more were found in the belly buttons of various participants in the study. The authors, led by Dr. Robert Dunn, identified over 2000 phylotypes (i.e., different types or species) of bacteria, most of which were rare and found in less than a tenth of the study’s sixty participants. No one particular phylotype was found in every person, but those that were common were shared by over seventy percent of belly buttons swabbed. What a bacterial ball!

We invited Dr. Dunn, the corresponding author of the study, to help give us some insight on the aptly named “A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, but Predictable”.


What was the impetus behind your research?

We originally started this project as pure outreach, to help people understand the wonderful ecological system that covers them from head to toe, inside and out. We found that people were very interested in seeing cultures of what lived on them but as we looked at the cultures it became clear there were more species (and simply more interesting things) growing on people than we expected. At some point the project went from outreach to science. […] Darwin got to […] go to the Galapagos, we decided to travel to the navel of the hair[y] guy who we see in the elevator sometimes.

Why choose belly buttons?

In our experience, the belly button is among the most ridiculous parts of the body. It is ridiculous enough that people who don’t necessarily like nature, say for example birds, can still be convinced to sample their belly button. […] The other reasons were more technical. The belly button is relatively less disturbed than, say, your hands. It is less exposed to all the chemicals and other people we bump up against during an ordinary day. In that way it is the closest thing we might find to an “old growth” sample of skin. Finally, it is worth noting that there are other body parts that are ecologically interesting but that we have found, and maybe this is just us being too old-fashioned, are awkward to sample at public science events.

What kinds of lessons do you hope the public takes away from the research?

That we know very little about the species on our bodies and around us in our daily lives. The species in your belly button or armpits, they are an important part of your first line of immune defense, and yet right now no one can explain to you why you have the species you have on your body. I know of no single study that is able to explain the differences in skin bacteria from one person to the next. That is a big mystery, not quite the pyramids of Egypt big, but big, and it is living and dividing on you right now. I’d like people to be more aware of that mystery and that the unknown, biologically speaking, is not just something far away, it is also the funny place that lint accumulates.

It is worth saying, in this context, that while we can now predict which bacteria tend to be frequent and common in belly buttons, we are  totally unable to predict which of the common species will be found on any particular person. Gender doesn’t seem to matter, nor does age, nor does innie/outie, nor does where you live now or where you were born. So that is what we are moving toward, trying to understand what governs the species that are found on any particular person […] and how we might alter our behavior in ways to favor species that keep us healthy and disfavor those that do us harm.

If others are interested in taking part or learning more about it, how would you recommend that they proceed?

Sign up at our mailing list and you can get emails about our next projects. Right now people can participate in projects on ants in their backyards, camel crickets in their basements and microbes in their kitchen, but as new mysteries turn up there will be more. Armpits, for example, are on the horizon. Oh, the armpits….

Participants in this study came from many walks of life: People curious about their spouse’s belly buttons, teachers wanting to find ways to engage their students in the microbial world around them, researchers, museum visitors, science writers and others. Read more of their stories at the links below:

If you would like to learn more about future projects you can visit the project’s home page: Belly Button Biodiversity.



Hulcr J, Latimer AM, Henley JB, Rountree NR, Fierer N, et al. (2012) A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, but Predictable. PLoS ONE 7(11): e47712. doi:10.1371/journal.pone.0047712

The image above can be found on the project’s home page.

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