Microbial Diversity in the Belly Button

In the tradition of those intrepid naturalist-explorers of the 19th century, join us on a journey into the uncharted territory that is the human belly button.

Consider first the vast landscape of skin in which your belly button is situated. Your skin, after all, is your body's largest organ – an organ that serves as a physical barrier to the outside world and an organ that is itself an ecosystem inhabited by thousands of microbial species. Most of these species are harmless, and in fact, many bacteria play protective roles defending you from pathogens that could make you very sick.

Environmental conditions – particularly moisture – can vary quite a bit across the landscape of our skin. Your forearm is a relative desert compared to the humid belly button. Accordingly, we find different kinds of bacteria living in different skin habitats, based on their preferred environmental conditions. For example, Staphylococcus and Corynebacterium prefer moist habitat and are, therefore, commonly found in belly buttons.

The skin is pocked with a number of glands whose secretions also shape its microbial community. Within the nooks and crannies of your belly button, three different glands are secreting substances that feed some bacteria and actively deter others. Eccrine glands secrete sweat, a substance composed of water, salt, urea, amino acids and small peptides (chains of amino acids). Some microbes feed on these amino acids while others are repelled by the small peptides. Sebaceous glands, associated with hair follicles, secrete an oily substance called sebum that coats the hairs and may actually deter the growth of some microbes. Apocrine glands produce a milky secretion that also appears to feed bacteria.

The habitat conditions of the belly button may explain why we generally find some microbial species to be more common than others in the navel, but as you'll see in the interactive graphic below, there is an extraordinary amount of variation among individuals. Some people have belly buttons dominated by one or two species whereas others have more even representation by handfuls of species.

This variation has really puzzled us. What factors determine the number and kinds of microbes we see in individual belly buttons? We've investigated some of the usual suspects like age, sex, ethnicity, innie vs. outie – even how often you report washing your belly button – yet we've been unable to sort out an answer to this question. We asked you to share your ideas and hypotheses, and we're now pursuing new analyses in quest of an answer. Perhaps there just isn't one.

Explore

We've gotten you started. Now it's time for you to explore your belly button.

Select your sample number from the dropdown menu. Hover over the pie pieces to see the relative abundance of a given species. Click the buttons next to the species names to remove dominant species and reveal smaller pieces of the pie.

What species are present in your navel?
What is the relative abundance of your common species?
Do some species dominate more than others?
Who are these species? You can learn more by reading profiles of the most common species.

Compare yourself to the "average" belly button to the right.
How different or similar are you?

Browse the charts of other participants.
What species do you have in common with others?
Are your common species more or less abundant than those found in others?
What factors do you think might be shaping these differences?

Can't find your sample? We analyzed belly button samples in two batches and thus built two different interactive pie charts. We recommend checking out the other interactive chart for your sample.

Tried that and still can't find your sample? Unfortunately, this means that something happened in the analysis pipeline such that we failed to get good quality DNA from your sample. This happens from time to time when we process a lot of samples. In some ways, our molecular approach is kind of like baking. If you make hundreds of cakes, every once in a while one just doesn't come out right.