The exact cause of endometriosis is not known, but researchers have some theories.
The female reproductive organs are shown with red patches representing endometriosis. The arrows indicate that the menstrual flow is going backwards into the fallopian tubes instead of out of the body as it should.
One theory suggests that endometriosis may result from something called "retrograde menstrual flow," in which some of the tissue that a woman sheds during her period flows through her fallopian tubes into her pelvis. While most women have some retrograde menstrual flow during their periods, not all of these women have endometriosis. Researchers are trying to uncover what other factors might cause the tissue to attach and grow in some women, but not in others.1,2
Researchers believe that endometriosis likely results from a combination of factors, including (but not limited to) some of the following:
- Because endometriosis runs in families, genes are probably involved with endometriosis to some degree.
- Estrogen (a hormone involved in the female reproductive cycle) also likely contributes to endometriosis, because endometriosis is an estrogen-dependent, inflammatory disease.
- In endometriosis, the endometrium may not respond as it should to progesterone, another hormone involved in the female reproductive cycle. This means that the endometrium has "progesterone resistance."
- In some cases of endometriosis, the immune system fails to destroy endometrial tissue, which enables it to grow outside the uterus. This means immune system dysfunction plays a role in these cases.
- Environmental exposures in the womb, such as to chemicals like dioxin and organochlorine pesticides, have also been linked to developing endometriosis.1,2
NICHD's Endometriosis: Natural History, Diagnosis, and Outcomes (ENDO) Study conducted by the Division of Intramural Population Health Research examines risk factors associated with endometriosis. The study has found evidence of increased risk of endometriosis associated with environmental exposures:
- Exposure to certain phthalates (chemicals used in plastics and other everyday products)3
- Exposure to certain industrial chemicals called "persistent organochlorine pollutants"4
- Exposure to some perfluoroalkyl and polyfluoroalkyl substances (PFAAs)5
- A specific ultraviolet filter (sunscreen) used in cosmetics6
- High urine concentrations of chromium and copper7
- Heilier, J. F., Nackers, F., Verougstraete, V., Tonglet, R., Lison, D., & Donnez, J. (2005). Increased dioxin-like compounds in the serum of women with peritoneal endometriosis and deep endometriotic (adenomyotic) nodules. Fertility and Sterility, 84, 305–312. PMID: 16084869 [top]
- Cooney, M. A., Buck Louis, G. M., Hediger, M. L., Vexler, A., & Kostyniak, P. J. (2010) Organochlorine pesticides and endometriosis. Reproductive Toxicology, 30, 365–369. PMID: 20580667 [top]
- Buck Louis, G. M., Peterson, C. M., Chen, Z., Croughan, M., Sundaram, R., Stanford, J., et al. (2013). Bisphenol A and phthalates and endometriosis: The Endometriosis: Natural History, Diagnosis and Outcomes Study. Fertility and Sterility, 100(1), 162–169.e2. PMID: 23579005 [top]
- Buck Louis, G. M., Chen, Z., Peterson, C. M., Hediger, M. L., Croughan, M. S., Sundaram, R., et al. (2012). Persistent lipophilic environmental chemicals and endometriosis: The ENDO Study. Environmental Health Perspectives, 120(6), 811–816. PMID: 22417635 [top]
- Buck Louis, G. M., Peterson, C. M., Chen, Z., Hediger, M. L., Croughan, M. S., Sundaram, R., et al. (2012). Perfluorochemicals and endometriosis: The ENDO study. Epidemiology, 23(6), 799–805. PMID: 22992575 [top]
- Kunisue, T., Chen, Z., Buck Louis, G. M., Sundaram, R., Hediger, M. L., Sun, L., & Kannan, K. (2012). Urinary concentrations of benzophenone-type UV filters in U.S. women and their association with endometriosis. Environmental Science & Technology, 46(8), 4624–4632. PMID: 22417702 [top]
- Pollack, A. Z., Buck Louis, G. M., Chen, Z., Peterson, C. M., Sundaram, R., Croughan, M. S., et al. (2013). Trace elements and endometriosis: The ENDO study. Reproductive Toxicology (Elmsford, N.Y.), 42, 41–48. PMID: 23892002 [top]