Scientists have found 1,400 strains of bacteria lurking in human belly buttons. The discovery was made during a study in which 95 volunteers allowed a team of microbiologists to gaze at their navels and take swabs from inside their belly buttons.
When the team behind the project checked the samples against a database of existing bacteria, they found 662 unrecognised strains, which might even be new species.
Although 1,400 different strains were found, 80 per cent were from 40 more common species. Many of the bacteria found were ordinary skin dwellers that are typically harmless. "We're probably the only ones studying human belly buttons on such a large scale," said project leader Jiri Hulcr of North Carolina State University when the study – Belly Button Biodiversity – launched in April.
As well as giving swabs, volunteers also submitted information about how often they clean their belly buttons, whether they have an "innie" or an "outie", as well as their age, sex, ethnicity and where they grew up.
Writing on the project's website, the team addressed the question many might be asking: why study the belly button? "Because everybody has one, it's what once connected us to our past. Yet, we barely notice it in our daily lives, to the point that few people actually wash theirs. Which is great for the bacteria," they wrote.
Among the volunteers to provide samples were New Scientist journalist Peter Aldhous and science writer Carl Zimmer. Some navels, such as Aldous's, were devoid of life, but Zimmer's belly button harboured "at least 53 species of bacteria".
After receiving his results, he wrote: "Several species I've got, such as Marimonas, have only been found in the ocean before. I am particularly baffled that I carry a species called Georgenia. Before me, scientists had only found it living in the soil. In Japan."
The team behind the project were keen to point out that the vast majority of these bacteria do no harm.
"We imagine germs as bad, and yet most are not. Most are either good or simply present," they wrote.
"The diversity on our bodies is, like any biological diversity, fascinating and full of awe and we want to share the joy of discovering it."
* In 2001, Karl Kruszelnicki, a physicist at the University of Sydney in Australia, found that 66 per cent of people observed a daily accumulation of navel fuzz.
* Like the fluff that collects in tumble dryers, most belly-button lint is a bluish grey. But other studies suggest the colour corresponds to that of the wearer's clothing, blue being a particularly popular choice.
* Your belly button is your very first scar. It is tissue left over from where your umbilical cord joined you to your mother's placenta when you were in her womb. Just like fingerprints, no two belly buttons are alike.
* The most abundant individual mass of lint was found in a 2009 study to be between 1.20mg and 1.29mg. According to the same study by the Vienna University of Technology, old T-shirts or dress shirts produce less navel fuzz than brand new T-shirts.
* Only 4 per cent of those who took part in the project had belly buttons which stuck out, with the rest all being "innies". The same microbes were found in both kinds, however.Reuse content