Please stop "vaginal seeding"
That's not how any of this works.
I want to take a second to address a very pervasive myth.
We DO NOT get most of our important gut bacteria when we pass through the birth canal.
This notion seems to have arisen with the observation that being born by C-section increases your chances of having gut issues later in life: a messed up microbiome. And this is true.
It’s also true that the vaginal tract is full of Lactobacilli. And since Lactobacillus is one of the very few kinds of “good” bacteria that most people know about, I can see how you’d come to the conclusion that this is where our gut bacteria come from.
So this has led to the practice of “vaginal seeding”. Well-meaning new parents who deliver by C-section will sometimes swab the vagina, then wipe the swab around on various body surfaces and in the mouth, to help give them the bacteria they missed when they didn’t pass through the birth canal. Some obstetricians apparently do this as standard practice, to the extent that the American College of obstetricians and gynecologists has issued a memo saying “cut it out".
It’s not likely to do much harm, but the “in the mouth” bit is misguided for a few reasons, and talking about why presents a good opportunity to talk about how we do get our gut bacteria, and what it implies.
The C-section / Dysbiosis Connection
Studies have found that the microbiome of a kid born by C-section is more likely to be missing important species than someone born vaginally, and that they’re more likely to carry opportunistic pathogens like Clostridium perfringens.
But consider all the things that go along with a C-section. Most importantly: it’s rare that a person undergoes a major surgery like that without receiving some kind of antibiotic. Often, these are given intravenously to the mother, and a 2019 Nature paper reported that, even if a child is born vaginally, giving a mom antibiotics during labor results in the infant having a microbiome that looks like a C-section baby’s, a few months out.
Also—and I do not invoke this argument casually—think about how unnatural a C-section is. Up until VERY recently, if you cut a person open four layers deep and pulled the living child out of her, what were her odds of survival? The maternal immune system is responsible for deciding which bacteria get to live in her body, and her child’s. After birth, it has to perform this incredibly delicate task—of ensuring that its newborn gets “infected” with all the bacterial species which it needs for protection and nourishment, but none of the pathogens.
So to make, at the start of that process, an assault on the mother’s body that literally ought to be deadly—throwing the immune system into full lethal alert mode—it’s like asking Noah to load up the ark while a wildfire is actively consuming everything within a forty mile radius. This might explain a recent animal study which showed that, even if a mother doesn’t get antibiotics during a C-section, her offspring’s gut microbiome is still less likely to be healthy than a naturally born counterpart.
All this to say: if you undergo a C-section, swabbing your pussy and smearing it around in your kid’s mouth isn’t gonna do them much good. The skin microbiome, I’ll grant—certainly, a large portion of this is seeded via the birthing process, so if you want to smear something, the kid’s pits and crotch could probably use it. But the notion that it’s vaginal bacteria getting into the mouth and nose, then down into the GI tract, then colonizing, is ridiculous for a couple of reasons.
For one, the vaginal microbiome is one of the least diverse in the human body. In a healthy vaginal microbiome, you’ll find mostly a few species of Lactobacillus, a sprinkling of other aerotolerant taxa—but none of the Bacteroides, the Clostridia, the Ruminococcus or Roseburia that typically make up a gut microbiome.
Bacteria are highly specialized to their ecological niche. The bugs that live in the vaginal canal are mostly good at preventing pathogen colonization, via production of things like lactic acid and hydrogen peroxide. Gut functions, like degrading plant polysaccharides, sequestering heavy metals, or producing the molecules that fuel your intestinal cells, are largely absent in them—for the obvious reason that you don’t typically find any of those things in a healthy vagina.
This has led some to try and patch the theory by suggesting that, well, women are also supposed to shit themselves while giving birth, giving the baby a chance to get exposed to all the mother’s rectal bacteria.
This is a…valiant effort of a hypothesis.
But it still leaves the problem that it suggests a messy, chancy process; there’s no guarantee that a given species of microbe in the mother’s gut would make it into the infant’s. Mother nature does not tend to leave terribly important things to chance.
The Contract
Many of the microbes in the human gut aren’t found anywhere else, so somehow these strains have made their way down across the generations, from whatever proto-human existed before our divergence from Neanderthals, all the way down into your and my guts—but how? Is it true that “everything is everywhere, and the environment selects”?
In about 2010, the first findings began to come out which suggested an elegant answer to this puzzle: milk.
For a long time, it was thought that breastmilk was sterile, and that any bacteria in it were contaminants from the mother’s skin, or the infant’s mouth. But with the advent of gene sequencing tech, we found that milk is teeming with bacterial DNA, representing most of the major taxa in the mother’s gut. This appears to provide a coherent explanation for the C-section/dysbiosis connection as well: a 2019 study reported that, even when no antibiotics are used in a C-section, it drastically changes the milk microbiome.
To my mind, this single fact—that a mother’s gut microbiome is reliably transmitted to her child’s—has such enormous implications for our understanding of evolution that it’s on par with the theory of natural selection. This guarantee of transmission to the next generation creates a kind of contract between microbe and host. It gives them a stake in our fitness, cutting them in on the returns: another generation of hosts to house them and perpetuate them. You’ll notice that this is virtually the same relationship we have with any of our genes.
When success for us came to mean success for them, in a Darwinian sense, those bacteria became a part of the human organism.
Yet, where the contract with your genetic DNA is more-or-less ironclad, antibiotics and infant formula have given us the ability to break our contract with our bacterial genes: shortchanging the next generation of biochemical pathways that no human has ever before had to do without, or accidentally deleting whole swaths of a person’s effective genome in the fight to eliminate a pathogen.
Some of these things, you might be fine without; maybe you get a food intolerance if you lose the enzymes that are supposed to break down certain complex carbohydrates. But others are necessary for things like metabolizing the amino acid phenylalanine, which is neurotoxic if the body can’t handle it properly.
At any time of life, losing capacities like that could be dangerous. If it happened during a developmentally critical window, you might see a normally-developing child suddenly start to regress mentally, to have wild immune system derangements, to gain or lose weight in a drastic way. It might look a lot like some of the diseases that have stymied medicine for the past fifty years.
Takeaways & Caveats
The fact that most of our important gut bacteria seem to come uniquely from other humans suggests that the “hygiene hypothesis” as it’s usually talked about is misguided. Letting your kids play in the dirt and put their mouths on escalator handrails is all well and good, but it’s probably not going to replace the key taxa that they’re supposed to acquire at home. If I had to guess, I’d say the main culprit behind our vanishing interior biodiversity has more to do with the fact that your average American now takes one course of antibiotics per year, rather than hand sanitizer reducing the amount of literal dirt in the diet.
Takeaways: Breastfeed your kids. Don’t pump and freeze, if you can avoid it, and don’t microwave-thaw frozen milk; there are living things in there. Don’t get a C-section if you don’t have to. Avoid antibiotics wherever possible. If you want your kid to be Baptized in Pussy, go for it I guess—but before putting the swab their mouth, think about how you’d feel if your own mom did as much to you.
As for caveats: There are confounding variables in all epidemiological studies. It’s true that women who have the ability to exclusively breastfeed their kid for six months are also likely to be more financially stable, able to depend on their partner’s income and take a hiatus from work to raise the child. These are fair objections, but even controlling for things like income, the data seems to bear out that breastfeeding reduces the risk of outcomes like obesity. This is not to say that a kid who doesn’t breastfeed, or who’s born by C-section, is doomed. Plenty of people develop a perfectly healthy microbiome just by living with a healthy family and friends. But it’s an odds game, and things like C-section reduce a kid’s odds of acquiring the full suite of “bonus” genes that we’re supposed to have. Antibiotics, of course, also have their place; there are times when their use is unavoidable—but I don’t think it’s controversial to say that they should be used far more sparingly than they are.
I know this is probably going to be an unpopular take, because it is taking a hard stance on both breastfeeding and natural birth, which have increasingly become viewed as “optional” over the past few decades. C-section is medically necessary in 10-15% of cases, but rates of C-section have risen higher than 50% in some parts of the world. (What the fuck, Brazil?) Breastfeeding is equally hairy. Not everyone can, and even those who are physically capable are usually subject to financial pressure to put ‘em on formula and get back to work.
I’m sorry to be the bearer of that news, if you’re a mother who took an elective C-section, or opted for formula earlier than you would have, if you’d known about the milk microbiome. Motherhood is already fraught enough without some asshole scientist coming along and telling you “Aha, we’ve just found out that you did it wrong!”
But we have to confront the facts that make us uncomfortable, if we want to do better in the future. The silver lining of discovering that we’ve done it wrong is that we begin to understand how to put those wrongs right.
In my dream of a bacterial-utopian society, we have a very well-funded version of La Leche League, some kind of wet nurse network where new mothers can support each other in helping their kids develop a healthy microbiome, even if one of them can’t breastfeed. For people who are just missing one or two key species, we’ve got milk-transmissible probiotics to fill the niche. If a child’s microbiome gets disrupted, say by a course of antibiotics during a developmentally critical window, their family has the knowledge and courage to do a home microbiome transplant, to set things back on the right course.
It’s easy enough to give someone a healthy microbiome. Not always pretty, but easy. It’s a living thing, and like any living thing, the microbiome is almost miraculous in its resilience—in how eager it is to take root and grow, if we simply give it the chance.
🖖🏼💩