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A 2012 study that collected samples from 60 belly buttons found almost 2,400 types of bacteria, with an average of 67 types per person. Most of these types were relatively rare -- that is, they were found in fewer than 10% of the belly buttons tested. In fact, not one type of bacteria was found in every belly button, but eight types are fairly common, showing up in more than 70% of the navel samples.