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New meaning to 'navel-gazing': Scientists study belly button bacteria

A group of scientists at North Carolina State University is taking navel-gazing to another level.

Jiri Hulcr and his colleagues at the Raleigh, N.C., school recently launched the Belly Button Biodiversity project as a fun way to interest people in microbiology and teach them about the bacteria that's found on skin.

Although the belly button is an unusual place to conduct research, in many ways it's ideal digs for germs.

"The belly button is protected, making it a safe haven for normal skin microbes," says Hulcr, a postdoctoral research associate who leads the project.

Another plus is that few people wash this area with soap. "That's great for bacteria," explains Hulcr, because you get more interesting things growing there. (So far, they've found lots of Staphylococcus epidermidis, which is the most common bacteria found on skin -- but also bright yellow colonies of Micrococcus luteus, and gooey globs of Pseudomonas.)

A third advantage is that the "belly button doesn't produce any special secretions or oils, such as other protected body parts, such as the nose or armpit," Hulcr says. "So the microflora inside the belly button is fairly representative of the rest of the body."

And it's easily accessible: To get a sample, researchers hand each subject a sterile long cotton swab. You're asked to turn it around in your navel three times and place the swab in a vial. Scientists grow the bacteria in a culture and once they become "big and chunky enough" they're photographed. Participants are given a sample number to view their bacteria online.

Volunteers also submit information about how often they wash their belly buttons, whether they have an "innie" or an "outie," as well as their age, sex, ethnicity, and where they grew up. 

"People are always surprised at how much stuff grows from even this superficial sample," Hulcr says, adding that a moderately disgusting discovery their project has made was that "very few people wash their belly button with soap."

In the nearly 500 samples collected since the project began in February, Hulcr says they've found the diversity of microbes you would expect to see on skin -- "almost universally bacteria, some molds and fungi, but not as many yeast as anticipated." (Finding yeast on skin is quite common.)

"We're probably the only ones studying human belly buttons on such a large scale," admits Hulcr. He hopes to collect thousands of swabs and eventually sequence a sampling of the bacterial DNA to identify each type -- and determine if there are noticeable differences between men and women, for example, or based on how often you clean your navel.

We conclude with a roundup of some random belly button trivia:

  • "Outies" are rare. Only 4 percent of project participants so far have them. (They don't have any different microbes, though.)
  • An Austrian chemist has suggested that people with hairier bellies collect more navel "lint."
  • Your belly button is a "lint" trap for fabric fibers from clothing as well as dead skin, fat, sweat and dust.
  • It's possible to have navel melanoma. Notice the size and shape of any mole you have there.
  • Research suggests the "ideal female belly button" is small and T-shaped. Less attractive navels are horizontal, protruding ("outies"), or have weird shapes.

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