Bacterial Ecosystems Abound On Our Skin Bacterial colonies flourish on human skin, occupying moist bellybuttons, oily brows and even the parched plains of the forearm. Skin scientist Julie Segre talks about mapping these diverse bacterial ecosystems ā€” and how the bacteria populations may affect skin health.
NPR logo

Bacterial Ecosystems Abound On Our Skin

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
Bacterial Ecosystems Abound On Our Skin

Bacterial Ecosystems Abound On Our Skin

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript


You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. A little bit later in the hour, the fascinating history of the telescope. It's not what you think it is. But first, as the weather gets hotter, with summer approaching, people are getting - yes, we travel in the subways - they're getting sweatier, and well, there is no delicate way of saying it, they're getting smellier too, I think.

Of course we all know that smell from bacteria in your armpit working overtime on a sweaty day, and in moist areas like your underarm, there can be as many as a million of them per square centimeter, but you may be surprised to learn that bacteria just don't thrive in the sweaty rainforest-like environment under your arms, they're all over your skin, between your fingers, behind your knee, on your forearm, and scientists are just now mapping out those colonies on the human body, and those bacteria are actually working for our benefit, believe it or not. They're going unappreciated and unwanted.

Here to talk about them and about research that's out this week in the journal Science is my guest, Julie Segre, senior investigator at the National Human Genome Research Institute. That's at NIH in Bethesda. Welcome to SCIENCE FRIDAY.

Dr. JULIE SEGRE (National Institutes of Health): Thank you, Ira. It's a pleasure to be a participant after being a listener for so many years.

FLATOW: Well, you're very welcome. Thank you for this research. How many bacteria are there? I don't think - were you surprised when you did this to find out how many there were?

Dr. SEGRE: I actually think I was surprised that there were this many bacteria on our skin. Iā€¦

FLATOW: Why do they want to live on our skin?

Dr. SEGRE: Well, nature abhors a vacuum. So there's little nooks and crannies for them to live, and I think we actually provide them a pretty good source of food.

FLATOW: 1-800-989-8255, talking about bacteria on our skin. A pretty good source of food, Doctor, what do you mean by that?

Dr. SEGRE: Well, the human body is really a super-organism. The bacterial cells that live in and on our body outnumber us 10 to one. Well, our human cells still weigh more than a bacterial cell, so we outweigh them, but they outnumber us, and I have to imagine that as a super-organism if the organism prospers, that's the human body, then the bacteria prosper and the human prospers, and we live together with them.

They eat the dead cells of our skin and the lipids, the oily products we produce, and we take benefit from them as well. These healthy bacteria are keeping away the ones that are pathogenic.

FLATOW: What do they - you know, if you eat something, you've got to put something down, you have to excrete something, right? So what do the bacteria leave behind after they're eating up all these oils?

Dr. SEGRE: Well, there is that one waste product that you referred to earlier that is the smell of the underarm. That is a waste product of the bacteria, but oftentimes what the waste products that they produce is really used to moisturize our skin and provide the necessary barrier of the skin, the barrier that protects the body from the more hostile environment than the bacteria. There's a lot of things out there that are worse than bacteria.

FLATOW: So we're spending all our time trying to get rid of the bacteria, and they're actually becoming moisturizers for us.

Dr. SEGRE: Natural moisturizers.

FLATOW: But those emollients we see on TV, we don't need them.

(Soundbite of laughter)

Dr. SEGRE: Well, I wouldn't go so far as to say we don't need them. We're - I mean, we are all aging, but the bacteria really do have a lot of benefit for us, and it's rather amazing to me that we're willing and wanting to eat probiotic yogurt, and then we're trying to sterilize our skin, when the real goal should be living in balance with the bacteria.

FLATOW: Where did you find most of the bacteria living?

Dr. SEGRE: The moist areas are really the places that the greatest number of bacteria want to live. The rest of the skin is a dry desert. The moist areas are very abundant in bacteria, and then there are some places like inside your nose and the belly button. Those are really rich in bacteria.

FLATOW: How - I'm afraid to ask. How diverse is this population? Is it just one strain or species or lots of them?

Dr. SEGRE: When we were looking at the bacteria by culturing it, we thought there were about 10 species of bacteria that lived on our skin, but it turned out that was a misconception that we knew, but we didn't know even how to approach it. So this study is based on the sequence of the DNA, and the sequences of the DNA is sort of like a signature for each bacteria.

We found 100 times more bacteria by sequencing than we can by culturing. So we found about 1,000 different species. Now, some of these bacteria predominate really in the moist areas or the dry areas or the greasy areas. So there is a lot of specificity. Now, obviously the bacteria that live in your underarm are really quite different than the ones that live on your forearm, and the interesting feature is that my underarm is more like your underarm than my underarm is like my forearm. Now that actually makes sense to us, but we had to figure that out.

FLATOW: Our armpits are more similar, yours and mine, than your armpit or mine and our forearm.

Dr. SEGRE: Absolutely, and it's because it's a very different ecosystem. The bacteria that can adapt to living in a moist, hairy environment are very different than the ones that want to live in a dry, arid desert.

FLATOW: And if we get rid of them by washing them away with soap and water, let's say, do they come back? They must come back, I imagine.

Dr. SEGRE: So I am a big believer in personal hygiene. I mean, if you knew how much time I spend harassing my kids to wash their hands, you'd believe this. But personal hygiene, it's really important. So we should wash the bacteria. Those are the transient bacteria. The resident bacteria live deeper in our skin than you could wash off, and then they live all the way down into the hair follicles, which are pretty deeply seeded into the skin. They live in the hair follicles, they live in the sweat glands. So there's no way that you're going to get rid of them.

When we try to swab the skin, we get rid of about 10,000 bacteria per square centimeter. We scrape the skin, like take your fingernail and really scrape off the top layers. We can get rid of 50,000, but there's a million bacteria per square centimeter. So you really couldn't get rid of more than one out of 20, even by really rigorous, you know, washing.

FLATOW: Let's take a call or two. Let's go to Zeb(ph) in Nashville. Hi, Zeb.

ZEB (Caller): Hey, how you doing?

FLATOW: Hey there.

ZEB: I was curious if the bacteria that is on our skin, if that plays into the pheromones and how we're attractive or not attractive to the opposite sex, and I'll take my question off the air.

FLATOW: All right, thanks. Good question. What do you think, or is that not your area, Dr. Segre?

Dr. SEGRE: Oh no, I mean, I think that this is all part of how we live as species, and I'm sure the bacteria do contribute to these sort of signals that we send to each other. I mean, we already talked about it as the sweat, but also the pheromones are produced by our human cells, but then they're sort of wrapped together with bacterial proteins that probably do contribute to the way we sense each other as individuals. That's - I mean from a research perspective, the skin is great because it's so accessible, but it's also just a very important part of how we present ourselves.

FLATOW: We did a story a little while back about bacteria growing on your skin, and we also found out that there were a lot of fungi growing there too. Do they live in harmony with each other?

Dr. SEGRE: They must be living in harmony for a long time, and there's a lot of interactions between the bacteria and the fungi. There's probably competition between them, but there's also collaboration.

FLATOW: And do you want to encourage then these bacteria to grow or not? Do you want to wear hot, sweaty socks to keep the colonies going?

Dr. SEGRE: I'm not sure that I would actually encourage that type of behavior. I think that we - probably as long as we just try to do everything in moderation, we can have a pretty healthy lifestyle. That's - but this is actually one of the things that we're trying to gain with the Human Microbiome Project that's being funded now as a new initiative from the NIH, is to really understand the role of the bacteria and the fungi in promoting human health.

FLATOW: Let's go to Judith in Chico. Hi, Judith.

JUDITH (Caller): Yes. I know that one of the benefits of healthy bacteria is they crowd out bad bacteria, and one of my real concerns is with the commercial promotion of antibacterial soaps, antibacterial sprays for our homes, that we are going to wind up developing drug resistance in these kinds of bacteria that we want to have, just like we're doing with our antibiotics and drugs and pharmaceuticals.

FLATOW: Do you agree, Dr. Segre?

Dr. SEGRE: So this project is about exploration. And it's exploring what is human health. And we are changing our environment so dramatically with the use of all of these antibacterial products. And that's why I really feel like we need to lose the language of warfare. We need to stop thinking of all of these bacteria as pathogenic. And I agree with Judith(ph) in that the bacteria like the Staph epidermidis stands on your skin. I'm here. I'm here. And it crowds out the Staph aureus which is more a pathogenic bacteria from adhering.

So we need to understand what is normal, healthy bacteria on the skin, and then I hope that there will be further tests to see how you really should be keeping that system in balance because you do need to practice good hygiene and remove the transient bacteria. But you want to keep the balance and not just wipe out all the bacteria on your skin.

FLATOW: We're talking about bacteria with Dr. Julie Segre. If you'd like to phone, our number is 1-800-989-8255. Also, you can tweet us, our Twitter is @scifri. Twitters questions are coming in.

What about MRSA. They're some of the really deadly germs out there, do they live normally on our skin but don't get in unless there's an opportunity for them to go through a cut or something?

Dr. SEGRE: Well, that is one of the big problems, is the MRSA infections. And a survey that has been published in the New England Journal of Medicine showed that there was one percent of Americans who are - have MRSA inside their nose. But these people don't have recurring infections. And one of the things that we're really interested to learn is whether it's the healthy bacteria that are keeping the MRSA in check. And that much as we are been talking about the probiotic yogurt, maybe it is this healthy bacteria that are keeping the pathogens, like MRSA, in check. And so we should be thinking about ways to overgrow them and promote health. But there are emerging pathogens out there that are really important for public health.

I think MRSA is very important and we screen in our hospital for it and I have a very - I'm very invested in the research on MRSA because I think that by understanding how MRSA infects, we can come up with really novel strategies for treating it.

FLATOW: You're listening to SCIENCE FRIDAY in NPR. I'm Ira Flatow. We're talking about bacteria this hour and talking with Dr. Julie Segre.

So we where would you like to go from here? Now that you're doing the survey, when you're done - or how soon will you be done - and what would you like to do next?

Dr. SEGRE: Well, this is part of a larger international consortium, the Human Microbiome Project. So it's really a team of us that are interested in very similar ideas. But this is a baseline. This is looking at healthy individuals and we really want to move as fast as we can to start thinking about how there might be shifts in the microbial community: in psoriasis, eczema, acne.

Now, the remarkable thing is psoriasis is on the outside of the elbow, eczema is on the inside of the elbow. Is that because there's different microbial community shifts that go on those two diseases? Well, in eczema, it actually is inside the elbow and it's behind the knee. And we found those two sides were the most closely related sites on the human body. So maybe that does begin to explain why eczema presents behind the knee and inside the elbow. So the goals of this project, really, is to move as fast as possible to really achieving clinical benefit for patients. I mean that is the goal of the National Institutes of Health is to use the taxpayers' funds to really come up with new strategies for promoting health and curing disease.

FLATOW: Mm-hmm. 1-800-989-8255. We know from speaking with people who do gardening, for example, we're talking about bacteria in the soil, it's very hard to culture bacteria in the laboratory. Over 90 percent of them won't grow in the lab. Is that why you're using the DNA sequencing in the technique?

Dr. SEGRE: That's exactly right. The bacteria that we can grow in the lab is very limited because we're not very good at mimicking this complex environments that they've adapted to on the skin. But now that we know who lives on the skin because of our DNA techniques, now we can actually figure out the conditions in the lab to grow these bacteria. And that's exactly what we're doing because, as I was saying, we just have a signature of these bacteria. Now we want to know all the proteins they encode.

FLATOW: Well, and do you want to know whether they grow better on certain people living in certain climates and other people too? Or another - people eat different foods, things like that?

Dr. SEGRE: There are so many possibilities that could be influencing how the bacteria take up residence on our skin. Maybe it's even from the beginning who was delivered by C-section versus a vaginal delivery. The number of possibilities - who has a pet who doesn't? I mean, the number of possibilities are really astonishing.

FLATOW: But can you actually look into those things?

Dr. SEGRE: Oh, yeah. I mean that's where having one baseline then opens the window to ask, are there differences between skin of a younger person versus a pubescent teenager versus an older person?

FLATOW: Well, let me ask you a very delicate question. How do you get these skin swabs from people? Do you have to be very delicate on how you ask for a sample in certain parts of the body?

Dr. SEGRE: Well, you should meet Maria Turner who's the chief dermatologist who has worked with us. And, no, the people are very - they're really okay about giving skin samples. It's much less invasive than giving a blood sample even, that a lot of people are accustomed to doing that. The skin is something that, yeah, we all have and it's not - I mean, we just use something like a Q-tip tip to get these samples.

FLATOW: Yeah, yeah. Well, thank you very much for taking time to be with us, Dr. Segre.

Dr. SEGRE: Well, thank you.

FLATOW: And good luck to you. This is a quite an interesting topic. We're all going to be looking at our skins and our hair follicles a little bit differently tonight.

Julie Segre is a senior investigator at the National Human Genome Research Institute. That is at NIH in Bethesda, Maryland.

We're going to take a break. When we come back, we're going to talk about the telescope. This is the International Year of Astronomy. Who invented the telescope and why? It's an interesting story with a long tale. So we'll be back to tell it after this break. Stay with us.

(Soundbite of music)

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

Copyright © 2009 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.