How does your navel compare

Talk about navel-gazing: Since February, a group of scientists at North Carolina State University has been studying the germs that inhabit our belly buttons as part of a study called the Belly Button Biodiversity project.

Sounds like an odd research project, but the belly button is the “ideal location” to study germs, says Jiri Hulcr, PhD, a postdoctoral research assistant who is heading the project.

“We’re trying to educate the public about the role bacteria play in our world,” says Dr. Hulcr. “Bacteria are always present on our skin and in our bodies. In fact, there are many, many more bacterial cells on and in our bodies than actual human cells.” (Each person carries about 100 trillion microbes; the human body contains about 10 trillion cells).

Unlike such body parts as the nose or armpits, the navel doesn’t secrete anything. Also, since most people tend to ignore their belly buttons — after all, you don’t scrub or exfoliate it like you do your face — navel bacteria tend to be untouched. “Believe it or not, the belly button serves as a good representation of the types of bacteria found on the body,” Hulcr says.

Good Germs and Bad Germs

The scientists so far have collected nearly 500 samples from belly buttons on cotton swabs, and posted magnified images of each person’s microbes on their Wildlife of Your Body Web site. You don’t need to be a biologist to notice that the cultures vary greatly from person to person.

So what types of bacteria inhabit our belly buttons? “All kinds!” says Hulcr, although his team has mostly found two common skin bacteria, Streptococcus and Staphylococcus, which he says are, for the most part, “friendly.”

“We absolutely need bacteria in order to survive,” he says. “It’s like asking an animal who lives in a forest if he needs the trees. The presence of bacteria is not harmful — it’s only under certain conditions when these bacteria can be potentially unhealthy, like if someone has lowered immunity or a skin injury, like a sunburn.”

The takeaway: Don’t be freaked out by your belly button germs.

More Belly Button Facts

We asked Hulcr and other experts to tell us everything you never knew about your navel. Here, the top seven fascinating finds:

  1. Innies dominate. Hulcr’s team asked study participants whether they had “innies” or “outies.” Only 4 percent of those studied said they had outie-shaped belly buttons.
  2. You can’t control whether you get an innie or outie. Technically considered a scar, belly buttons mark the connection of a mother’s umbilical cord to her fetus in the womb. “The cord serves as the unborn baby’s lifeline, providing her with vital food and oxygen and removing waste products like carbon dioxide,” says Karen Marie Jaffe, MD, an obstetrician-gynecologist affiliated with the University Hospitals of Cleveland. The cord is clamped immediately after birth and the remnant eventually falls off to unveil the belly button.The ultimate shape of the belly button depends on a number of factors, according to Indianapolis plastic surgeon Barry Eppley, MD, including how the scar attaches to underlying muscles, the looseness of surrounding skin, the fat under the skin, and how flat or protruding your belly is. “Belly buttons vary greatly in their size and shape,” he says on his blog, Explore Plastic Surgery.
  3. Your belly button shape can change — under one special circumstance, pregnancy. “The expansion of the abdomen can cause some “innie” belly buttons to pop out and become outies, but most often, there is not much change in the structure itself,” says Dr. Jaffe. And after birth, the belly button often retracts to its former shape.