IN SHORT: If you have unprotected sex with a man, does the DNA from his semen stay in your body "forever"? No, of course not. There's no evidence for this science-adjacent Facebook claim.
"If you have sex with a man, his DNA lives in you forever," reads a message circulating on Facebook since September 2022.
The message's argument is that, through a process called microchimerism, a man's semen ejaculated into a woman during unprotected sex leaves his DNA inside her, forever.
DNA, short for deoxyribonucleic acid, is a kind of code that instructs the growth and development of organisms from people to trees to insects.
The message adds that the man's DNA will enter the woman's bloodstream, brain and spine. Over time, it says, the DNA will change the woman's cells.
Microchimerism is the presence of a small number of cells from one individual in the body of another individual. The phenomenon has been found in people, as well as in monkeys, pigs, rodents and sheep.
Studies have shown that microchimerism can occur in several ways. One is during pregnancy, when Y chromosomes (male gene cells) from a male foetus cross the placenta and enter the mother's bloodstream.
The original claim mentions a 2005 study published in the American Journal of Medicine that was carried out by researchers from the Fred Hutchinson Cancer Research Center in Seattle, a city in the US state of Washington.
The 2005 study does mention that sexual intercourse may be a possibility through which male cells could be transferred to a woman through semen, when a condom is not used.
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Is this enough to support the claim that the DNA in semen lives in women "forever"?
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The 2005 study tested 120 women without sons for the presence of male cells in their bodies. The women were grouped according to pregnancy history i.e. women who had only daughters, women who had spontaneous abortions, women who had induced abortions and women who were never pregnant.
It found that microchimerism was high in women who had abortions.
Although mentioned as a possibility, the study did not specifically test whether the male DNA found in women without sons was transferred to women during sex. Nor did it find that male DNA transferred this way lived in the body of women and roamed freely in her bloodstream as claimed.
When Africa Check spoke to Natalie Myers in 2019, then the spokesperson for the Fred Hutchinson Cancer Research Centre told us there was "no evidence the DNA is from sexual partners".
An Australian Associated Press fact check looked into similar claims in 2021. It quotes a lead researcher at the Fred Hutchinson Cancer Research Centre, Prof J Lee Nelson, as explaining that there was no data to support the claim.
Nelson said that "if this were routinely happening ... you would see (male microchimerism) in the vast majority of women that we studied".
The claim - that when a man has unprotected sex with a woman he leaves a part of his genetic cells inside her via his semen - is unproven.
