A new truth about Lady Gaga’s health has recently been revealed. She is covered in other life-forms—“her little monsters” you might call them. Contrary to statements otherwise in the media, these life-forms have nothing to do with Lady Gaga’s meat bikini. (For those who need the extra explanation, Lady Gaga is perhaps the most popular music personality in the world. A meat bikini is, well, unfortunately just what it sounds like.) Long before she strapped on her sirloin, her prevailing condition was contaminated. You can take the girl out of the country, but you can’t take the bacteria out of the girl’s large intestine. But before you get holier than thou, I should point out that the condition with which Gaga is afflicted is the human condition. We are all covered in other species, gowns of life far more outrageous than a few strips of wayward meat. Here then are the 10 life-forms you (and Lady Gaga) are most likely to be wearing this spring.

1. Just dance

We’ll start at the bottom. At least from a distance, feet can be lovely. They bend and twist to hold us up and move us over the world. Each foot is composed of 26 bones, every one intimately articulated with one or more others. But confronting a foot toe-on presents dirtier realities. The feet contact everything we hold our snootier noses up and out of (one feels, for the poor ants who must taste, in part, with their tarsi). Even when they are fully cloaked in socks, shoes, or--if you are Gaga--feathers, they are still a biome unto themselves. They are tougher and warmer, but also damper than most of our parts. With tens of thousands of sweat glands per inch, our feet sweat to excess. They are the poor man’s rain forest and like the rain forest, they abound in fungi. But it is not just any fungi that grows around our toes. Oh no, it is a special one. Tricophyton rubrum, the most common foot fungus, feasts on dead skin and toenails. It, or one of its close kin, is worn by many of us, perhaps most, of us. It blossoms from our flotsam. Every so often, when its garden grows too much, it becomes “athletes foot”; fungal bodies grow like the leaves of grass and as they do, the toe nails yellow and the skin cracks. But most of the time T. rubrum’s growth is moderate. It is neither friend nor foe, simply a freeloader, a wayward child left to forage where no one else will go. Wiggle your toes and, whether you are wearing flip-flops or Prada, your fungi wiggle, too.

Alongside the filaments of our fungi live bacteria. The bacteria on our feet consume the amino acid leucine found in sweat. It is these amino-acid-eaters that cause feet to stink. In eating leucine, these creatures excrete a gaseous perfume (isovaleric acid) that is instantly recognizable as it rises up from under the table. The stinking bacteria on most of our feet are Staphylococcus epidermidis, but those of us with especially stinky feet may also host another species of bacteria, Bacillus subtilis, which, despite its name, stinks with a ferocious lack of subtlety.

So far, we have scarcely begun to study the life down under in our home bound antipodes. It simply grows, mates and dies, between your toes. If you cannot afford to go to remotest Papua New Guinea to find a new species of brown bird, bend down and touch your feet. As you do, you will undoubtedly lay hold of at least a few species that no scientist anywhere in the world yet knows anything about, your own special ornament. And when you do, they will probably smell. Maybe this is what Neruda meant when he described "the lost bouquet of your body." Maybe not.

2. Fancy pants

Move from the foot on up the legs and fungus becomes rare. Our legs are dry like a desert and so require special adaptations for habitation. But a few proud forms have persevered. Alright, more than a few. Perhaps a trillion organisms live on your exposed skin, perhaps 10 trillion, perhaps more. They are as thick as pants. The astronomer Carl Sagan often waxed about the billions of stars, but closer to home is an even greater multitude of spherical forms, each of them exhaling, eating and dividing. Among the most common of these microbes are two species of Staphylococcus, Staphylococcus hominis and S. aureus. In some cases, these and other bacteria on our exposed skin can be bad, worse, or even deadly. Most days though, they seem to be good. Our skin microbes can provide us with a layer of defense, a moat around our corporeal castle. Perhaps it is because they eat the food that pathogens need to establish and in doing so prevent them from settling our shores. Perhaps not.

Whatever the rest of the story is, it will take decades to resolve. More research seems to add more complications. Several studies have mapped the distribution of particular species of bacteria on our bodies, but historically such studies considered only bacteria that could be grown in the lab. As of the last five years, we now know that most of the bacteria on our bodies cannot be grown in the lab. When new genetic approaches are used to “see” what is living on us, they find tens or even hundreds of kinds of microbes not noted before, many of them previously unknown to science or known to science only by the the code of their genes (map image from Bibell and Lovell 1976). Nearly two hundred kinds of bacteria have been found on human forearms alone, where it was thought that there were fewer than a dozen. Just as with older studies, these new studies tend to find different microbes in different parts of the body (the bacteria in the hair seem very different, for example). Yet, just what these many life-forms are doing is anyone’s guess. Some are probably bad. Some are probably good. Others may simply be tourists, pausing in route to some more distant shore. Whatever they are doing, they are doing it on you. Scrubbing your exposed surfaces with soap changes the species that are most common (tending to kill the most abundant species and make space for the rarer forms), but it does not make our bacterial robes go away. Reconcile yourself--whether you are Gaga or the guy next door, the outfit you wear a living gown, but it is not meat. It is microbial. It will always be.

3. Bad romance

Moving up, let’s not pause too long near the (meat) bikini line other than to say that our privates are riotous with life. They are what conservation biologists tend to call a “biodiversity hot spot.” Our nether regions (or is it nether lands?) are even more tropical than our feet. It is here that many organisms that can live nowhere else on us find safe haven. There are the genital lice (AKA crabs, Pthirus pubis) that although rarely mentioned at dinner parties, remain common. Their closest living relative is not our head or body lice, but instead a large louse found on gorillas (suggesting a lack of discretion on the behalf of one of our ancestors, since such lice are passed almost exclusively during sex). Where these crabs clamber, there is also the potential for a rich diversity of diseases (herpes, syphilis and kin), each of which takes advantage of our most predictable point of junction. Along with our pathogens live many, many, guests, most of which do no harm, or are too poorly known to say one way or another. Each private nook, cranny and niche has its own particular species. The bacteria species that live in vaginas, for example, are almost exclusively of the Lactobacillus group. A whole tribe of scientists is now studying these bacteria (and nothing else--such is the specialization of modern biology). Among the questions on their minds is why these bacteria are so different from one woman to the next and whether such differences predispose some women to vaginosis (a kind of microbial community malfunction) while protecting others. The answer to the second question appears to be yes, but it is not yet clear why. Intriguingly, consistent differences in vaginal bacteria exist among ethnic groups, though again, why, how and to what ends no one knows.

4. Out of control

Moving on back, your colon has, in addition to those jokes and half-truths you pull out at parties, an enormous quantity of life in it. Thousands of kinds of bacteria, archaea, viruses (including bacteriophages) and, odds are worms (globally, most humans still end up with worms at one point or another), have crawled up and found a place to call home. The diversity of worms that potentially inhabit you is astounding, both in kind and form. Some have terrible grasping “heads”, others are short and twisted. Still others grow dozens of feet in length. Side by side, they are a gallery of demons and gods, but the worms are just the showy megafuana. There are more microbial cells in your colon and, heading up through your intestines, than there are human cells in your body. You are, by most reasonable accounting, more them than you. And so when someone says that you are full of it, rest assured that the “it” in question is bacteria and other inhabitants. We are just beginning to figure out what all of these microbes do. Sometimes they steal. Sometimes they cause harm. Most of the time though, it seems much of what they are doing is a mix of stealing and providing. They take some of what we have and provide, in exchange, that which we do not have (mostly key vitamins, such as K). In addition, they might help to protect us against other, less friendly, microbes. Although the number of species of bacteria in our intestines and colons is high, they tend to come from relatively few major bacterial lineages. The most common lineages in your intestines and colon are probably those of the groups Firmicutes and Bacteroidetes, each of which is also common in the guts of monkeys, cows, cats and rats. The human brain may be special (though not that special…), but our colons, well, less so.

5. Vanity

The belly button is under-rated as a subject of a study, the most modest of our crevices. For as much though as it looks like a cave, it seems as though it must have company over. It is known that the belly button can host bacteria (most similar, one study found, to those of the back of the knee). Recently, Jiri Hulcr and Britne Hackett, a postdoc and student in my lab respectively, set out to bring this lesson home. They sampled the fungi and bacteria of the belly buttons of folks in my lab for a holiday card. No fungi grew, but bacteria did, on some more than others. Benoit Guenard, my sole French student, was the most, how do I put this, bountiful (image left), though Jiri himself was a close second (image right, photos by Jiri Hulcr). Whether Benoit’s bacteria are uniquely French, we do not yet know. Time, and a few more French belly buttons should tell. Right now we are trying a broader sampling with the idea that we might one day set up a microbial sampling station at the new Nature Research Center in Raleigh, North Carolina, that you too might know what is eating at you (or at least off of you).

6. Glitter and grease

Your lungs, like your feet and nether regions, are somewhat warm and wet. But they are far removed from the food we eat. The organisms in our lungs have evolved to take advantage of the chemicals our trachea produce, however difficult they might be to use. Inside your lungs is a kind of fungi called Pneumocystis. It cannot live outside of human lungs. No one has been able to grow it anywhere else. What does it do in there? It appears to steal both amino acids and cholesterol from us, its hosts (Most of us seem to have too much of the latter anyway….). In healthy individuals, it has little true cost. It is only when we are sick with other diseases, particularly those such as HIV that compromise the immune system, that these fungi become a problem. In those cases, the fungus turns deadly, overgrowing its natural bounds. How Pneumocystis infects us is unknown. It may pass from lip to lip. More likely, it hovers in the air, flying into us as we walk through its clouds.

7. Blueberry kisses

The plagues in our mouths are bacteria, of many species, that link themselves together to hold on and take advantage of the waves of food that wash over them. These communities of different life-forms come together for their mutual benefit. Two species of Streptococcus, S. sanguis and S. mutans are the most commonly sampled and studied, but your mouth, like the rest of you, is really a kind of wild kingdom, for which your food is the primary production, the bacteria are the consumers and a variety of other life-forms are the top dogs. Protists, for example, live in your mouth, eating bacteria. Also, bacteriophages, a special form of virus that subsists on single-celled organisms, thrive. The bacteriophages use bacteria in the way the cold viruses use us, to get by.

8. Poker face

I will wager that Lady Gaga’s head is crawling with mites. They live in her pores and come out to have sex under the shade of her wig while she is on stage. Well, not just then. They do it other times too. She could have more than one kind of mite. Forehead mites (Demodex spp.) have not been well studied and they are so small that differences among species might be impossible to detect simply by studying how they and their parts look under the microscope (which is all that has been done). Where these mites have been studied, they have mostly just been counted. They are more common on older people than on younger people. The exception to this pattern is among the Tokelau islanders where the pattern is the reverse (more mites on younger people) for reasons unknown. On average--the Tokelau Islanders in the audience notwithstanding--more than half of us have forehead mites and quite a few of us host two species. Some of us may even host as of yet unnamed species. Every so often these mites are badly behaved (they are linked to rosacea, although innocent until more convincingly proven guilty), but mostly they seem to have no effect on our lives. Maybe they are even good for us? Who knows? What is clear is that they bury themselves in our pores and eat. Whatever it is they are getting, they have been getting it for millions of years and given that no one is really actively studying them, they seem likely to continue to do so, for millions more, our persistence permitting.

9. Love games

I hesitate to even tell you that you may have brain parasites. In these bad economic times, no one needs something else to worry about. Yet, they could be in there, wedged deeply between your ears. I am talking about Toxoplasma gondii, a parasite of cats. Toxoplasma gondii is able to reproduce only when it is inside the gut of a cat. It needs to find a cat, really bad. Usually it does so by finding something that cats eat, such as rats. Inside rats, it makes its way to the brain where it causes the rats to be attracted to the smell of cat pee, which they would ordinarily avoid (who wouldn’t). A rat that follows cat pee is likely to find a cat and when it does to end up in the cat’s gut, where the Toxoplasma gondii can finally mate. But T. gondii also makes its way into humans (It is because of this parasite that pregnant women are urged to avoid cat litter). In fact, sixty million Americans are estimated to be infected at any one moment. How long T. gondii has been common in humans is uncertain. When T. gondii finds its way to us it either dies or goes into a dormant state, to wait. When T. gondii takes these endearing little naps, it triggers the release of chemicals in our brains that make us more anxiety prone, decrease our reaction time and make us more likely to end up in dangerous situations, like the mouth of a large cat. Many of our ancestors may have made it, under such circumstances, into the guts of cats. Death by leopard or lion was once very common. But now that being eaten by a cat is rare (Vegas performers excepted) T. gondii simply affects our behavior without any benefit to itself. Whether Lady Gaga has Toxoplasmosis is hard to say, though somehow it seems as though it might explain her outfits.

10. Changing skies

Dust mites live in our beds, feeding off the skin that flakes from our bodies each day. No one understands the biology of dust mites well (and so be suspicious of anyone who promises to get rid of them for you). There are many species. Two species of the genus Dermatophagoides are most common in the developed world. Others are more common in the tropics. And yet any given pillow might house as many as a dozen different kinds of mites, each with a different history and story. They float into our lives like an ether of legs and mouthparts. Something about our stationary modern ways has made them even more common than they once were in the caves of our origins. A pillow’s weight, it is sometimes said, can be as much as half mites and mite feces. Such simple metrics of their invasion into our lives are crude and hard to verify and yet capture the essence of our circumstances, surrounded by eight legged creatures so small they turn up unnoticed in our lungs, hair and nearly everywhere else. Some have suggested these species even breed in some of our lungs. Maybe. Others have suggested that they don’t breed in our houses or bodies at all, but instead just blow in with the winds of our air conditioners and heaters. Maybe. Or maybe there are eggs all around you. No one knows. Though I swear that at night when I listen carefully I hear them hatching in my bed, one by one, to eat what I no longer need.

11 to 11,000. Royal treatment

Of course, there are more than 10 life-forms living on us. Tens of thousands of species at least occasionally live on some human, somewhere. In tropical regions, the possibilities are more diverse than in cold climates, but everywhere we are covered with things we have scarcely begun to study. The naked emperor or superstar may indeed have been clothed the whole time in a garment visible only to those in the know, but now I’ve told you and so you should be able to see too, what is really covering Lady Gaga, your mother, brother, husband, wife or sister. I have not even described the most intimate of our partners. There are the varicella zoster viruses that cause chicken pox in us when we are kids and then hang around in us, dormant in our nervous systems, for the rest of our lives. If you ever had chicken pox, you have this virus alive in you right now. It rears up again, as shingles, when we are weak and/or old. There are also pieces of ancient viral DNA lodged detritally here and there alongside your genes. There are mitochondria so intimately linked with us, in our cells, that without them we would die. Each mitochondrion is the vestige of an ancient bacterium. And more, and more, and more and more.

Lessons can be learned from the life that coats us, inside and out. We might learn tolerance of others, or at least of the others on us. We might learn to appreciate how poorly known the world still is, even the world of our own bodies (a topic I have written at book length about elsewhere, in Every Living Thing). But perhaps the greatest lesson is that no matter where and how we live we remain connected to the rest of life, dressed in other species. What we can choose is not whether to wear this life, but instead which species we will wear. Until now, we have tended to choose to kill as many of the species on us as we can. We scrub, we wipe, and we spray. In doing so we have favored the species that survive despite us. We have surrounded ourselves with such species. They are in our pillows and carpets and all around us in our cities. Think bedbugs, but also pigeons, rats, houseflies and house sparrows. An intelligent species might live amongst the species that are most beneficial to it, or at least most beautiful. In some ways, our body might be doing this. It is known that antibiotics, for example, can be found in sweat and that some of these antibiotics are somewhat selective in which species they kill. It is also known that compounds are being produced in our guts, by our bodies, to favor bacteria. Maybe our bodies are managing the life on us, for our benefit. But if they are, they are at odds with what our conscious minds are up to. Our conscious minds cultivate beauty and food far away and the resistance of weeds nearer at hand.

And so maybe Lady Gaga was on to something when she cloaked herself in another species, she was just making visible what goes on every day less conspicuously. Even if she takes her meat dress off, she is still covered in life. Bacteria shimmer on her lips and hips. The fungi on her feet lap up her sweat and the mites on her head, they don’t give a damn. They just bury their faces further into their one true occupation. They do so without glamour, pretense or agents, as they have for millions of years.


*Special thanks to the microbe-cloaked lab of Noah Fierer at the University of Colorado, Boulder, for insight into belly buttons, microbes AND for a list of the titles of Lady Gaga’s songs.

Katsutoshi, A. 2006. Foot odor due to microbial metabolism and its control. Canadian journal of microbiology 52 (4) 357-364; DOI 10.1139/W05-130

See, for example, the most recent study of the evolution of these organisms… Microbiology 153 (2007), 3466-3477; DOI 10.1099/mic.0.2006/004929-0

Bibell, D. J. and D. J. Lovell 1976. Skin Flora Maps: A Tool in the Study of Cutaneous Ecology. The Journal of Investigative Dermatology (yes, there is such a thing) 67 (2): 265-269.

Gao, J., Tseng, C., Pei, Z., and M. J. Blaser. 2007. Molecular analysis of human forearm superficial skin bacterial biota. Proceedings of the National Academy of Sciences. 104 (8) 2927-2932; doi:10.1073/pnas.0607077104

Costello, E.K., C.L. Lauber, M. Hamady, N. Fierer, J.I. Gordon, R. Knight. 2009. Bacterial variation in human body habitats across space and time. Science. 326: 1694-1697

Bäckhed, F., Ley, R. E., Sonnenburg, J. L., Peterson, D. A. and J. I. Gordon. 2005. Host-bacterial mutualism in the human intestine. Science. 307:1915-1920.

Reed, D. L, Light, J. E., Allen, J. M. and J. J. Kirchman. 2007. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice. BMC Biology. 5(7) doi:10.1186/1741-7007-5-7 (title="">http://www.biomedcentral.com/1741-7007/5/7)

Ravel, J. et al. 2010. Microbes and Health Sackler Colloquium: Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Sciences. doi:10.1073/pnas.1002611107

Van Woerden, H. 2004. Dust mites living in human lungs - the cause of asthma? Medical Hypotheses 63 (2) 193-197. The main table in this paper lists the mites that have been found in human lungs, if you are curious. It is a mighty long list (sorry).

Hallas, T. E. 2010. House-dust mites in our homes are a contamination from outdoor sources. Medical Hypotheses 74 (5) 777-779. Regardless of whether the conclusions in this article hold, I love that there is a journal called “Medical Hypotheses.” For the sake of full disclosure, it might more reasonably be called “Wild Medical Hypotheses.

About the Author: Rob Dunn is a science writer and biogeographer in the Department of Biology at North Carolina State University. His first book, Every Living Thing, told the stories of the sometimes obsessive, occasionally mad, and always determined, biologists who have sought to discover the limits of the living world. His new book, The Wild Life of Our Bodies, explores how changes in our interactions with other species, be they forehead mites or tigers, have affected our health and well being. Rob lives in Raleigh, North Carolina with his wife, two children, and more than two forehead mites.

 The views expressed are those of the author and are not necessarily those of Scientific American.