What Is Endometriosis?

Myth: it's the uterine lining itself, just in the wrong place

Close, but not quite. The tissue found outside the uterus in endometriosis resembles the endometrium — the lining that builds up and sheds each cycle — but it isn't identical to it. These patches most often turn up in the pelvis: on the ovaries, behind the uterus, and on the surfaces lining the pelvic cavity, though other sites are possible too. Because this tissue responds to the same hormonal signals as the lining inside the uterus, it thickens and breaks down with the cycle — only there's nowhere for it to go. That trapped cycle of swelling and irritation is a big part of why the condition can hurt, and why symptoms so often follow a monthly pattern.

Here's a myth worth retiring: severe period pain is not just "a bad period" that everyone has to push through. The short explainer video at the top of this page — just under four minutes long — introduces the condition plainly: tissue similar to the lining of the uterus growing where it doesn't belong, and why that causes trouble month after month.

Fact: the pain doesn't always match the amount of tissue

This surprises a lot of people. Someone with only a few small patches can have pain that disrupts work, school, and sleep, while someone else with more extensive tissue may notice very little. So the story you tell your clinician — when it hurts, where, and what it stops you doing — matters at least as much as any scan picture. Pain is commonly pelvic and tied to periods, but it can also show up around ovulation, during sex, or when going to the toilet, depending on where the tissue sits. Tiredness and difficulty conceiving are also reasons people first get checked. None of these signs on its own proves endometriosis, which is exactly why it can take time to pin down.

Myth: a normal scan means nothing is wrong

Not necessarily. An ultrasound can pick up some forms of the condition — for instance, a type of ovarian cyst associated with endometriosis sometimes called a chocolate cyst, because of the old blood inside it — but a clear scan doesn't rule the condition out, particularly for smaller or surface patches. Assessment usually starts with your history and an examination, and imaging may follow. In some cases a clinician may discuss laparoscopy, a keyhole look inside the abdomen, which lets the surgeon see patches directly and, where appropriate, treat them during the same procedure. If you want to see what treating visible tissue involves, this site's endometriosis excision video shows a laparoscopic excision being performed.

Fact: there are options, and the plan is personal

There's no single route that suits everyone, because the right plan depends on your symptoms, your priorities, and whether pregnancy is something you're hoping for now, later, or not at all. Broadly, clinicians may discuss pain relief, hormonal treatments that quiet the monthly cycle driving the tissue, surgery to remove patches, or a combination over time. It's a long-term condition for many people, so think of management as an ongoing conversation rather than a one-off fix. It also helps to know how it differs from operations covered elsewhere on this site, such as a hysterectomy — removing the uterus is a separate decision with its own reasons, not the default answer here. If period or pelvic pain regularly rearranges your life, that in itself is reason enough to raise it with a clinician and keep raising it if answers don't come.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician and researcher.

Frequently Asked Questions

What causes endometriosis?
The honest answer is that the exact cause isn't fully settled. Several explanations are discussed — including menstrual blood flowing backward through the tubes into the pelvis — but no single theory explains every case, and having the condition is nobody's fault.

Can endometriosis affect fertility?
It can make conceiving harder for some people, depending on where the tissue is and whether it affects the tubes or ovaries — but many people with endometriosis do conceive. If you're trying and it's taking longer than expected, it's worth mentioning early to your clinician.

Does endometriosis go away after menopause?
Symptoms often ease after menopause, when the hormonal cycle that drives the tissue stops, but that isn't guaranteed for everyone. Any new pelvic pain or bleeding after menopause should always be checked promptly in its own right.

Is surgery always needed to diagnose it?
No. Clinicians often build the picture from symptoms, examination, and imaging first. Laparoscopy is one way to see patches directly and is generally discussed when it would change management, not as an automatic first step.

Educational only — this article is general information about endometriosis, not medical advice. Persistent pelvic pain, very painful periods, or difficulty conceiving should be discussed with a qualified clinician, who can examine you and advise on diagnosis and treatment.