Allegation:
Women absorb and store the DNA of every man they have sex with.
Evaluation:
In late February 2024, a claim that women “hid DNA from every man” they had sexual intercourse with spread on X (formerly Twitter):
Nothing in the article above contains any biological truth.
The claim, which has been circulating on the Internet for years, stems from research into a phenomenon in which male cells are present in female human tissue: male microchimerism. Most, but not all, cases of this condition are the result of tissue harvested from pregnancy with a male fetus. Although the source of male DNA in women who have never experienced pregnancy is an ongoing question in science, sexual intercourse is only one speculative source of male microchimerism.
The same claim has gone viral several times since 2012, often as a defense of conservative social policies. Snopes first confirmed the claim in June 2017, when the website known as Your News Wire (now goes by many names, including The People’s Voice) published an article stating, “Women Absorb and Store the DNA of Every Man They Have Sex With.” “
This article claimed that a “new study” showed that cells transferred from a man to a woman during sexual intercourse integrated into that woman’s body “every time” after sex. In fact, the study they reference, published in PLoS ONE in 2012, revealed male microchimerism in female brain tissue in 63% of the 59 women the researchers analyzed postmortem.
These researchers did not draw any conclusions about the possibility of male microchimerism resulting from sexual intercourse, and their research was inconclusive. The importance of the paper was that it showed that male cells were able to cross what is known as the blood-brain barrier, a semi-permeable membrane that prevents most chemicals in the blood from entering the brain. In fact, sexual intercourse is not mentioned even once as a proposed mechanism in this study. Here’s what the 2012 study reached in terms of the source of these cells:
Most likely male source [microchimerism, Mc] It is the acquisition of fetal Mc in the female brain from pregnancy with a male fetus. Male DNA can also be obtained from women who have no sons through abortion or miscarriage. In the current studies, except for a few subjects, their pregnancy history was unknown, so there was male Mc in the female brain. [tissue] could not be evaluated based on previous specific pregnancy history. In addition to previous pregnancies, male Mc can be acquired by a female from a recognized or lost male twin, from an older brother, or through non-irradiated blood transfusion.
A paper published in 2015 explored this issue in more detail and concluded that potentially all of these potential mechanisms could contribute. This article, whose data set is quite limited, makes it clear that sexual intercourse transfer of male chimerism remains entirely speculative:
Data suggest that male microchimerism in teenage girls may result from a full-term older brother, an aborted pregnancy, or a blood transfusion during pregnancy. We think sexual intercourse may be important, but young girls probably have other sources of male cells.
Research conducted since Snopes’ original fact check in 2017 has shed some, but not much, light on the origins and significance of male microchimerism. For example, a study conducted in September 2021 reconfirmed the existence of male microchimerism in women who have never been pregnant. While the authors accepted the hypothesis that sexual intercourse could be a source, they said their study could not answer this question and suggested other alternative hypotheses:
Our study shows that the origin of microchimeric cells may not necessarily be a close family member. One source is sequential fetal-maternal exchanges repeated over generations. Other possible sources include unreported or unrecognized interrupted pregnancies, breastfeeding, placental structure, pregnancy complications including preeclampsia, and it has also been suggested that sexual intercourse may also play a role. We were not able to provide these data to a sufficient number of participants for a comprehensive analysis of these alternatives.
Collectively, all science can say for sure is that most—but not all—women have some male cells in their tissues, and that many—but not all—of these cases involve pregnancy with a male fetus. Science cannot answer definitively whether sexual intercourse is a potential source of male cells in cases where pregnancy does not occur, but it cannot say with certainty that a woman will “store the DNA of any man who enters her private parts unprotected.” Science isn’t even sure that such a phenomenon occurs.
This claim is False because the science underlying the claim that women preserve the DNA of all the men they sleep with is misrepresented.
Resources:
Chan, William FN and others. “Male Microchimerism in the Human Female Brain.” PLoS ONE, edited by Martin Gerbert Frasch, vol. 7, no. September 9, 2012, p. e45592. DOI.org (Crossref), https://doi.org/10.1371/journal.pone.0045592.
Funke, Daniel. “Fact Checkers Debunked This Fake News Site 80 Times. It Still Posts on Facebook.” Poynter, July 20, 2018, https://www.poynter.org/fact-checking/2018/fact-checkers-have-debunked-this-fake-news-site-80-times-its-still-publishing-on- Facebook/.
Johnson, BN et al. “Male Microchimerism in Females: A Quantitative Study of Twin Lineages to Investigate Mechanisms.” Human Reproduction, vol. 36, no. 9, August 2021, p. 2529–37. DOI.org (Crossref), https://doi.org/10.1093/humrep/deab170.
Müller, Amanda Cecilie et al. “Microchimerism of Male Origin in a Group of Danish Girls.” Chimerism, vol. 6, no. 4, October 2015, p. 65–71. DOI.org (Crossref), https://doi.org/10.1080/19381956.2016.1218583.
Yan, Zhen et al. “Male Microchimerism in Sonless Women: Quantitative Evaluation and Correlation with Pregnancy History.” American Journal of Medicine, vol. 118, no. 8, August 2005, p. 899–906. DOI.org (Crossref), https://doi.org/10.1016/j.amjmed.2005.03.037.