Researchers know that pain is a primary symptom of endometriosis, but it is not known how pain arises in women with endometriosis.
The severity of pain does not correspond with the number, location, or extent of endometriosis lesions. Some women with only a few small lesions experience severe pain; other women may have very large patches of endometriosis, but only experience little pain.3,4
Current evidence suggests several possible explanations for pain associated with endometriosis, including (but not limited to)3,4:
- Patches of endometriosis respond to hormones in a similar way as the lining of the uterus. These tissues may bleed or have evidence of inflammation every month, similar to a regular menstrual period. However, the blood and tissue shed from endometriosis patches stay in the body and are irritants, which can cause pain.
- In some cases, inflammation and chemicals produced by the endometriosis areas can cause the pelvic organs to adhere, or stick together, causing scar tissue. This makes the uterus, ovaries, and fallopian tubes, as well as the bladder and rectum, appear as one large organ.
- Hormones and chemicals released by endometriosis tissue also may irritate nearby tissue and cause the release of other chemicals known to cause pain.
- Over time, some endometriosis areas may form nodules or bumps as they create lesions on the surface of pelvic organs or can become cysts (fluid-filled sacs) on the ovaries.
- Some endometriosis lesions have nerves in them, tying the patches directly into the central nervous system. These nerves may be more sensitive to pain-causing chemicals released in the lesions and surrounding areas. Over time, they may be more easily activated by the chemicals than normal nerve cells are.
- Patches of endometriosis might also press against nearby nerve cells to cause pain.
- Some women report less endometriosis pain after pregnancy, but the reason for this is unclear. Researchers are trying to determine if the reduction results from the hormones released by the body during pregnancy, or from changes in the cervix, uterus, or endometrium that occur during pregnancy and delivery.
Pain from endometriosis can be severe, interfering with day-to-day activities. Understanding how endometriosis is related to pain is a very active area of research because it could allow for more effective treatments for this specific type of pain.
Reference: National Institute of Child Health and Human Development
Last updated April 20, 2017
1 American College of Obstetricians and Gynecologists. (2008). Endometriosis. Washington, DC.
2 Tietjen, G. E., Bushnell, C. D., Herial, N. A., Utley, C., White, L., & Hafeez, F. (2007). Endometriosis is associated with prevalence of comorbid conditions in migraine. Headache, 47(7), 1069-1078.
3 American College of Obstetricians and Gynecologists. (2008). Endometriosis. Washington, DC.
4 Stratton, P., & Berkley, K.J. (2011). Chronic pelvic pain and endometriosis: Translational evidence of the relationship and implications. Human Reproduction Update, 17(3), 327-346.