If you’ve spent virtually any time on the interwebs, and particularly lurked in the social media areas of this marvel of human ingenuity, you’ll no doubt at one point or another come across the fact that many women have living male cells hanging out in their bodies, including in their brains. The most common explanation, according to social media, for how these instances of microchimerism came to be is that women acquire these cells via making the beast with two backs with a man. The claim that often follows this is that, given these cells and their replicates have been shown to sometimes hang around for decades in the women, that most women have the DNA of every male sexual partner they’ve ever had in their bodies.

But is any of this actually true?

As with the vast majority of “quick facts” spread around on social media, there are elements of truth to it, but the part that makes the fact spread does not appear to be true at all based on the current state of scientific research. Unlike the effect of having unprotected social media, which will always leave residual undesired things in your brain, having sex with a guy doesn’t seem to be a contributor, or at least not a major contributor, to male cell lines finding their way into women’s bodies and brains. So how do these cells get there and where did the rumor that women retain the DNA of every man they ever slept with start?

To begin with, back in 2012 a study titled, Male Microchimerism, noted that after dissecting a number of deceased women’s brains, 63% of the brains (37 out of 59) had male microchimerism present. While it was touted by many a media source that this was a huge discovery, in fact, it has long been known that a large percentage of women eventually carry living male cell lines in their bodies. For example, a study in 1969, published in The Lancet, showed that 70% (21 of 30) pregnant women, 19 of whom were pregnant with boys and 2 others having previously had boys, were found to have male microchimerism.

From there countless other studies have shown the same thing, including some animal studies that showed some of these cell lines are able to cross the blood-brain barrier in mice. What made this particular 2012 study interesting was simply that it was the first to show these cell lines could cross the blood-brain barrier in humans too.

It’s also interesting to note from this study that 33 of the women had Alzheimer’s and that these women had lower likelihood of having male microchimerism present. And even those who had Alzheimer’s AND male microchimerism, they tended to have lower concentrations of these cells. More on this and the potential benefits and drawbacks of this microchimerism in the Bonus Facts in a bit.

In any event, noteworthy here is that despite explicitly stating the likely sources of these cell lines- mostly centered around pregnancy- at no point in the study did the researchers state that these came from former sex partners. And as for the pregnancy source, the researchers speculate this may be how the cell lines are getting past the blood-brain barrier in the first place. As they state, “Changes in BBB permeability occur during pregnancy and may therefore provide a unique opportunity for the establishment of [microchimerism] in the brain.”

So how did this study become the source of the myth that women retain the DNA of every sex partner they’ve ever had? Enter Baxter Dmitry, a man who has the personal tagline “Speaking truth to power since he learned to talk…” and noting that he’s “travelled in over 80 countries and won arguments in every single one”. Naturally, a person who speaks such truth would write on a website, Your News Wire, that itself had the tagline “News. Truth. Unfiltered.”

With all that advocating for truth, it should come as no surprise that in June of 2017, Baxter published a completely unbiased, truthful piece on Your News Wire titled Women Absorb and Retain DNA from Every Man They Have Sex With using a study that literally said none of this as his primary source for that belief…

As for how he got around this little problem of the researchers not even hypothesizing this, using his masterful debating skills famed in 80 countries the world over, Baxter states of the researchers’ actual suggested sources of this male DNA,

Researchers assumed that the most likely answer was that all male DNA found living in the female brain came from a male pregnancy. That was the safe, politically correct assumption. But these researchers were living in denial… the scientists didn’t know what the hell was going on. Confused, they did their best to hide the evidence until they could understand and explain it. They buried it in numerous sub studies and articles, but if you sift through them all you will find the damning statement, the one line that gives the game away…

This “one line that gives the game away” is from a 2005 study, Male microchimerism in women without sons. In this study, they found that 21% of the 120 women they looked at had male microchimerism. Of these women, 26 of them had daughters; 23 had spontaneous abortions; 23 of them had induced abortions; and 48 of them had never been pregnant that the women were aware of. The results were the first group who only had daughters had an 8% rate of male microchimerism. The second group with spontaneous abortions had a rate of 22%; the third group with induced abortions had a rate of 57%; and the final group who’d never been pregnant were at just 10%, similar to the group who’d only had daughters.

How does this support Baxter’s claim? In this study, along with mentioning the more likely origins of this microchimerism, they also hypothesize that it may be possible some of these cases could be from having sex partners of the male persuasion. They offer no supporting evidence of this, simply speculating for potential further research.

From that one, then unstudied hypothesis presented in the paper as the least likely possibility, and completely dismissing the many, many other studies on the subject, Baxter naturally gave the unfiltered truth that this proved women retain the DNA from not just some, but every single man they ever had sex with. And that- we don’t know, for reasons we guess?- the researchers of the 2012 study were trying to hide this fact from the world.

He also made another lesser talked about rather… we’ll say “interesting”… claim we’ll get to shortly. But before that, as for the main claim, given this information has a grain of truth, is claimed to be backed by a scientific study (which few are going to bother to read), is mildly plausible on the surface, or at least not readily debunkable by the layman without looking into it a little, and is incredibly eye catching in headline form, it naturally spread throughout the various social media outlets whose algorithms and platforms cater to content with no depth or nuance, like Facebook and Twitter.

Now, you’d think that’s where it would end given this particular little “fact” using the 2012 study as its supposed source takes only about 10 minutes to call its accuracy into question via even just skimming the cited study. But it turns out a large percentage of popular general news sites don’t actually bother to have their authors read the studies they are reporting on, with this little rumor functioning as a great test to see which outlets do and which outlets don’t.

And so it was that many of the most popular general news outlets’ reported that the researchers in the study claimed the source of the DNA in women’s brains was from sexual partners. Some of the worst offenders even doubled down and went with the full supposed fact that the study showed women retain the DNA of many or ALL of their previous sex partners.

This finally brings us to where the DNA is actually coming from. As briefly alluded to, pregnancy seems to be the #1 source, though it turns out it doesn’t necessarily need to be the pregnancy of the woman in question. Because these cell lines from the fetus can survive for decades after the pregnancy, subsequent pregnancies a given woman has can then see some of these cell lines find their way into the new little.

Demonstrating this cellular exchange, directly after pregnancy, approximately two thirds of women will carry fetal immune cell lines, for example. On the flipside, about 1/3 of the time the baby will have maternal immune cell lines after they are born.

Illustrating all this, we have such research as a 2015 study Microchimerism of male origin in a cohort of Danish girls, looking at 154 girls 10-15 years old. Unfortunately for adding a more definitive data point to the question at hand, the researchers did not ask the girls if they’d had sex before, though given their age, it can be presumed that the majority had not. Delving into this, the researchers note that in a separate study it was shown that approximately 16% of 14 year old girls in Denmark have had sex, and a total of 36% have done so by age 15. Importantly, however, 80% of these 14/15 year old girls who had sex reported their partner used a condom, which limits the possibility of such cell transfer.

In any event, the results of this study on 10-15 year old girls showed that 13.6% of the girls tested positive for male microchimerism, which is more or less inline with the previously mentioned study of adult women who’d either only had daughters or never been pregnant, with rates of about 8% and 10% respectively. This also almost exactly lined up with another study on prepubescent girls, with about 14% testing positive for male microchimerism in that study.

As other studies have also shown, the 2015 study researchers also noted that girls who had older brothers were more likely to test positive for male microchimerism, with the more older brothers, the more likely to test positive. They also found girls whose mothers had blood transfusions during pregnancy were more likely to test positive as well.

Given this data set, however, the researchers do note that they could not account for all the instances of male microchimerism based on the known data and, thus, further research is needed to figure out where all these cells lines are coming from more definitively.

To date, it isn’t actually fully clear what is happening here for these unaccounted for cases. The leading hypotheses is that these are probably coming from things like cases of a vanished and unobserved male twin or, more likely in most cases, a woman, including the mothers of these girls, having been previously pregnant with a boy and they simply didn’t know it. It turns out, depending on what study you want to go with, between 1/3 and just under 1/2 of all human pregnancies result in a miscarriage, with a decent percentage of these happening without the woman actually knowing she was briefly pregnant. Further, a large percentage of the rest of these miscarriages happen before the sex of the baby is known.

That said, given researchers have not yet definitively been able to account for all these sources of male microchimerism, it’s always possible it could be from a sex partner, and more research is needed to figure this out definitively. But at present, this is deemed unlikely.

Why?

It turns out, it’s a massive conspiracy backed by the Lizard People…

Or for those of you who want to continue to allow our Lizard overlords to pull the wool over our eyes, when talking the “every partner” narrative, this can conclusively be shown to be false with the known data given that if that were true, virtually every heterosexual woman should test positive for male microchimerism. This is not the case.

But even when just looking at unprotected sex partners, where there is indeed some brief surface level cellular exchange happening for both partners, most researchers still find this an unlikely source, as the vagina is an incredibly inhospitable place to try to establish a cell line in the first place, including being relatively rapidly self cleaning and good at getting rid of such offending cells.

And even if some cells still managed to find their way into the bloodstream, via, say cuts in the vagina or the like, these would in the vast majority of cases be identified and eliminated by the woman’s immune system. Fetal cells, on the other hand, can potentially have ways around this problem.

As summed up by Dr. J Lee Nelson, co-author of the aforementioned 2012 study that is the commonly cited source of this myth, “any suggestion that male DNA is routinely retained from sexual partners has no support from any scientific study… the biggest statement is the data; if this were routinely happening… you would see it in the vast majority of adult women (without sons) that we studied.”

We should probably also address very briefly that some have, very bizarrely, gone further and claimed it’s the sperm themselves that manage to survive and live on in the women. But, of course, sperm don’t replicate themselves and only last at most a week or so. So, no. Just no.

And how that rumor got started… Well, that was in Baxter’s original piece that started the main rumor in the first place. To quote the legendary debater,

Sperm is alive. It is living cells. When it is injected into you it swims and swims until it crashes headlong into a wall, and then it attaches and burrows into your flesh. If it’s in your mouth it swims and climbs into your nasal passages, inner ear, and behind your eyes. Then it digs in. It enters your blood stream and collects in your brain and spine. Like something out of a scifi movie, it becomes a part of you and you can’t get rid of it.

Given that this part is easily debunkable without any research needed by the vast majority of even high school educated humans, it goes to show you that the over 70,000 people who shared his post on the subject didn’t bother to read the source of the “fact” before sharing it.

Now, all this said, if you twist the wording of the headline “women retain the DNA of the men they sleep with” enough, you could say a man who got a woman pregnant does have a part of his DNA surviving in her thanks to the joined genes from the sperm and egg then producing a fetus that then spreads certain of its cells in the woman, some of which survive long term. But, at least, when talking about the common full headline- “Women retain the DNA of every man they’ve ever slept with,” this is conclusively false, even when talking having sex without a condom. And while research may someday show this can potentially happen in some very isolated cases, though again among other factors the woman’s immune system makes this implausible, the body of evidence to date definitively shows it can’t be common, else by the twilight years of most heterosexual women’s lives there would be an almost 100% rate of male microchimerism, even in women who’d never had older brothers nor been pregnant with boys themselves.

Thus, as ever when having unprotected social media, always remember the wise words of the great Wheezy Waiter, in his sage song “A Headline’s Not an Article”–

A Headline’s not an article, a Tweet is not an article. It’s basically a farticle, of a full-blown pooped out article.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

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• Can You Really Just Go Online and Order a Wife from Some Other Country?
• How the Weird British Tradition of Putting Topless Women on the Third Page of Newspapers Got Started
• Why Women Fainted So Much in the 19th Century

Bonus Fact:

Speaking of the potential health benefits and drawbacks of these fetus sourced cellular lines hanging around in women’s bodies, women with lupus erythematosus that also have male fetal cell lines in their bodies have been shown to have consistently better functioning renal systems vs those women without these male fetal cells. This, and many other studies, seem to indicate in some cases these fetal cell lines might actually help in repairing damage to certain body parts.

Similarly, it’s long been known that pregnancy ultimately reduces a woman’s chance of both getting and dying of breast cancer. Why isn’t clear. But relatively recent research has shown that certain fetal cell lines concentrate in this breast tumor tissue, with it being hypothesized this may be having a positive effect. Other studies have similarly shown a potential benefit to fetal cell lines to women who later develop certain other types of cancers, with similar congregation of the fetal cells in the tumors. Again with all of this though, how this is helping, if at all, isn’t fully clear. And in some cases it’s been speculated to actually INCREASE the chances of getting certain cancers. Obviously much more research is needed to determine any of this definitively.

Also on that flipside, the effect of these cell lines in a woman’s brain have been proposed as a possible reason women are more susceptible to certain neurological disorders. Likewise, these cell lines have been speculated to be increasing the chances of certain autoimmune disorders that women are more susceptible to.

That said, there is one neurological disorder, mentioned in the aforementioned 2012 study, and also in several others, where the presence and high concentration of fetal microchimerism seems to strongly correlate to less chance of developing the disorder- that being Alzheimer’s. Though, again, as with pretty much everything to do with this field of study right now, significantly more research is needed to determine anything definitive.