GUY RAZ, host:
We're back with ALL THINGS CONSIDERED from NPR News. I'm Guy Raz.
Right at the moment of birth, a baby's skin is like freshly tilled soil. She's designed to absorb all kinds of microbes and bacteria from her mother, bacteria that might help scientists understand why babies born via caesarean section are more prone to certain conditions like asthma and allergies.
Well, a research team led by the University of Colorado at Boulder found that babies who pass through the birth canal and those delivered via C-section are exposed to very different types of bacteria.
One of those researchers is Elizabeth Costello. She is now at Stanford, where she explained what they found.
Ms. ELIZABETH COSTELLO (Researcher, Stanford University): The adult human body is home to trillions of harmless and even beneficial bacteria, but we don't start off life that way. We start off life as sort of a blank slate, microbiologically speaking.
When a baby is born, he or she emerges from an environment that is generally microbe-free into a world where microbes are everywhere. And at that point, the colonization process begins.
What we and others found, that the first bacteria that a baby encounters and also the degree to which we can say where those bacteria come from depends a lot on delivery mode.
RAZ: So when a baby is born via C-section, say, which bacteria are they not being exposed to that are beneficial?
Ms. COSTELLO: Well, I'm not sure about what's beneficial or not at this point. However, they're not exposed to vaginal bacteria. And when a baby is born via that route, he or she is essentially coated in these kinds of bacteria, which are unique to that habitat, for example, lactobacillus.
When a baby is born via caesarean section, he or she isn't exposed to those microbes and is exposed to different kinds of microbes. We found that those microbes looked a lot like what you would find on the human skin surface.
RAZ: So earlier research has suggested that, you know, C-section babies might be more prone to things like asthma or having allergies or other immune system-related conditions. But your study doesn't necessarily reinforce that theory?
Ms. COSTELLO: I would say it doesn't. So those theories relate to the hygiene hypothesis, which posits that the more we restrict our exposure to microbes, the less our immune system understands how to deal with them appropriately.
What we show simply is that there's a difference based on delivery mode in the microbes that a baby is exposed to in the first moments of life. Whether or not those differences contribute later on is something that further studies will have to address.
RAZ: Elizabeth Costello, C-sections obviously have shot up in recent decades. I think it's something like a third of all deliveries in the U.S. now, right? Is that about right?
Ms. COSTELLO: That's about right.
RAZ: For many women, obviously for babies as well, it's a life-saving technique, it is necessary, required.
Ms. COSTELLO: Absolutely.
RAZ: Is there a way to expose a C-section baby to the bacteria that they would be exposed to if they were delivered vaginally? And would that make sense?
Ms. COSTELLO: Well, it might make sense. If further studies do demonstrate that there's a beneficial effect of being exposed to particular kinds of bacteria from the vagina, then one could imagine a future scenario where babies born via C-section are exposed to a particular kind of probiotic in order to facilitate that exposure.
RAZ: So where do you take the study from here? I mean, obviously, the implication is that those bacteria from a mother are beneficial to the baby. We don't know that for sure, but we have to possibly assume that that's the case. And if that is the case, and if the baby does need those bacteria, where do you take the research from here?
Ms. COSTELLO: Well, as a microbial ecologist, where I want to take this research is simply just to look at what happens in healthy babies over time as they grow older.
I think that we know what happens now in the minutes after delivery. We're starting to know very much about what adults look like. And I think filling in that timeline in between really just to see if these bacteria that are initially there persist, I think, is a really interesting question.
RAZ: That's Elizabeth Costello. She's a postdoctoral researcher of microbiology and immunology at Stanford University.
Elizabeth Costello, thank you so much.
Ms. COSTELLO: Thanks so much for having me.
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