... The project got a set of volunteers to run a cotton swab through their belly buttons, and then looked at all the bacterial species growing there. The results suggest that the belly button is a diverse environment, and the communities living there respond to the habits of their host. Notably, a few species that were discovered for the first time on human skin were found in an individual who hadn't bathed in a few years.
That's from Belly Button Biodiversity finds no two navels are quite the same by John Timmer.