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What Causes Endometriosis?

In spite of the various claims on the internet, no one knows the cause of endometriosis.

“The definitive cause(s) of endometriosis remain under heavy debate, though demonstrated association with a number of hereditary, environmental, epigenetic and even certain menstrual characteristics exist. Current research implicates HOX genes, mesenchymal stem cells and certain immunologic factors in disease origin; nonetheless, no single theory explains endometriosis all those affected; more likely, a composite of several mechanisms is involved.” [Quote from the Center for Endometriosis article: Endometriosis: a Complex Disease]

Retrograde menstruation

Also known as Sampson’s theory, this theory is that menstrual blood leaks out of the tubes into the pelvis and these bits of endometrium implant themselves in the pelvis where they land and grow into endometriosis. This 100-year-old theory has never been proven, and in fact, has an enormous amount of evidence against it as the cause of endometriosis. I did 2 in depth Instagram posts about some of the evidence against retrograde menstruation here and here. The most damaging aspect of retrograde menstruation is that many ineffective treatment options are based on this unproven theory, at a detrimental cost to us patients. I talk about this in an Instagram post here. Evidence is stacked against retrograde menstruation as the (unproven) cause of endo, yet many cling to it like its truth. Even if retrograde menstruation did play a small role in endo for some people, it’s literally impossible for it to be the main cause like many in the medical community say it is.


While there are several theories to the cause of endometriosis – and there may indeed be multiple factors and causes playing into why a person has it – one theory of origin is Mulleriosis/Metaplasia. This proposes that endometriosis is due to a developmental defect in the formation of the Mullerian duct system when we are embryos (with involvement of the HOX genes). The Mullerian duct is the very beginnings of the reproductive system that will later form the fallopian tubes, uterus, uterine cervix, and superior aspect of the vagina. Cells that are laid down during its formation may have abnormal migration (they may not go to the right spot) or abnormal differentiation (when a cell changes from one cell type to another) and later develop into endometriosis.

In fact, in one study endometriosis was found during autopsy in fetuses assigned female at birth (who died for other reasons) at around the same rate, 10%, that it is found in the adult population of people assigned female at birth today.

The theory of embryonic origin can explain:

  • how endometriosis can be found anywhere in the body.

  • how endometriosis has been reported in the medical literature in around 20 people assigned male at birth. (And in fact the numbers are probably higher than 20, since it’s likely some cases were probably found but not published in medical journals.) This could be because as embryos, we have the beginnings of both the (what’s considered) “male” and “female” reproductive tracts during the first 6-8 weeks in the womb. Typically, one regresses and the other develops, so that the embryo has that specific set of reproductive organs. However, cells from the reproductive track that regressed can remain behind.

  • why endometriosis is found in embryonic patterns in the body and has low recurrence after complete excision.

Genetic Component

There is thought to be a genetic component to endometriosis. Multiple studies have found there’s an increased risk of endometriosis if a family member or relative has the disease.

Recently, a 2023 study by Rahmioglu el al. called The genetic basis of endometriosis and comorbidity with other pain and inflammatory conditions observed “significant genetic correlations between endometriosis and 11 pain-conditions including migraine, back, and multisite chronic pain (MCP), as well as inflammatory conditions including asthma and osteoarthritis.” (1) This study looked at the genetic correlation between endometriosis and 32 immune/inflammatory, pain, reproductive, and metabolic traits/conditions. It’s also worth noting that none of the autoimmune conditions showed significant genetic correlation with endometriosis.


  1. Rahmioglu N, Mortlock S, Ghiasi M, Møller PL, Stefansdottir L, Galarneau G, Turman C, Danning R, Law MH, Sapkota Y, Christofidou P, Skarp S, Giri A, Banasik K, Krassowski M, Lepamets M, Marciniak B, Nõukas M, Perro D, Sliz E, Sobalska-Kwapis M, Thorleifsson G, Topbas-Selcuki NF, Vitonis A, Westergaard D, Arnadottir R, Burgdorf KS, Campbell A, Cheuk CSK, Clementi C, Cook J, De Vivo I, DiVasta A, Dorien O, Donoghue JF, Edwards T, Fontanillas P, Fung JN, Geirsson RT, Girling JE, Harkki P, Harris HR, Healey M, Heikinheimo O, Holdsworth-Carson S, Hostettler IC, Houlden H, Houshdaran S, Irwin JC, Jarvelin MR, Kamatani Y, Kennedy SH, Kepka E, Kettunen J, Kubo M, Kulig B, Kurra V, Laivuori H, Laufer MR, Lindgren CM, MacGregor S, Mangino M, Martin NG, Matalliotaki C, Matalliotakis M, Murray AD, Ndungu A, Nezhat C, Olsen CM, Opoku-Anane J, Padmanabhan S, Paranjpe M, Peters M, Polak G, Porteous DJ, Rabban J, Rexrode KM, Romanowicz H, Saare M, Saavalainen L, Schork AJ, Sen S, Shafrir AL, Siewierska-Górska A, Słomka M, Smith BH, Smolarz B, Szaflik T, Szyłło K, Takahashi A, Terry KL, Tomassetti C, Treloar SA, Vanhie A, Vincent K, Vo KC, Werring DJ, Zeggini E, Zervou MI; DBDS Genomic Consortium; FinnGen Study; FinnGen Endometriosis Taskforce; Celmatix Research Team; 23andMe Research Team; Adachi S, Buring JE, Ridker PM, D’Hooghe T, Goulielmos GN, Hapangama DK, Hayward C, Horne AW, Low SK, Martikainen H, Chasman DI, Rogers PAW, Saunders PT, Sirota M, Spector T, Strapagiel D, Tung JY, Whiteman DC, Giudice LC, Velez-Edwards DR, Uimari O, Kraft P, Salumets A, Nyholt DR, Mägi R, Stefansson K, Becker CM, Yurttas-Beim P, Steinthorsdottir V, Nyegaard M, Missmer SA, Montgomery GW, Morris AP, Zondervan KT. The genetic basis of endometriosis and comorbidity with other pain and inflammatory conditions. Nat Genet. 2023 Mar;55(3):423-436. doi: 10.1038/s41588-023-01323-z. Epub 2023 Mar 13. PMID: 36914876; PMCID: PMC10042257.

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