What is endometriosis? Symptoms, pain and why the disease is still overlooked

What is endometriosis? In short, it is endometriosis a chronic disease, where tissue resembles (important note - reminds of, not is) whether the uterine lining grows outside the uterus.

190 million. That's how many people with a uterus live with the disease endometriosis worldwide. 1 in 10 menstruating women suffer from endometriosis. And despite its prevalence, it still takes an average of 7 years to be diagnosed with endo, as it is colloquially called. 

Maybe you've never heard the word before and are sitting there thinking: Endo-what-what?
Or maybe you're one of those who nods in recognition of menstrual cramps from hell – the disease's defining characteristic.

In this article, we delve into the often overlooked disease endometriosis and take a closer look at what it really is, why it can hurt so much – and why too many people still go around with symptoms for years without getting a diagnosis.

This article was written by Emma Libner, author, vaginal activist and sexologist, it is updated with new knowledge in 2026 by Cathrine Wichmand

What is endometriosis and what does it mean?

The name comes from the Latin word for uterine lining, endometriumIn endometriosis, tissue that resembles this mucous membrane tissue appears in places in the body where it doesn't really belong.

It could be, for example, on:

• the ovaries

• peritoneum

• the intestines

• the bladder

And in rare cases even further away from the uterus in the body.

The special – and problematic – thing is that this tissue behaves almost exactly like the uterine lining. It responds to the body's hormones.

As the menstrual cycle progresses, the endometriosis tissue follows suit: It grows, changes, and may bleed when menstruation occurs.

The only difference is that the blood from the uterus has a natural outlet. The blood from endometriosis does not - and it can be painful. 

---

Why does endometriosis cause pain?

When endometriosis tissue bleeds inside the body, the blood becomes trapped. This can irritate the surrounding tissue and create inflammation. The body responds by sounding the alarm – and the alarm often comes in the form of pain.

And it can be very severe pain - debilitating for some.

Endometriosis is also not picky about its location. As described above, it can attach itself to the organs it comes into contact with. This means that tissue sometimes grows together in places where it shouldn't.

For example, in some cases, the ovaries and intestines can grow together. Here, the endometriosis tissue acts almost like Velcro, causing organs to “stick” to each other.

As the disease progresses, the pain can also become chronic – and in some cases occur throughout the month, not just during menstruation.

👉 Read more about menstrual cramps and how you can naturally reduce them.

---

Symptoms of endometriosis

Endometriosis can manifest itself in many different ways. Some experience severe symptoms. Others have the disease for years without knowing it. 
Typical symptoms may include:

• severe menstrual pain

• pain during intercourse

• ovulation pain (read more about ovulation pain here)

• chronic pain in the lower abdomen

• problems with bowel movements or urination

• bloating and stomach problems

• pronounced fatigue (pain also greatly affects our sleep quality)

• infertility

Let's dwell on fatigue, a symptom that is often overlooked. 
But when the body is constantly working overtime and struggling with inflammation and pain, energy stores can quickly become depleted. Chronic fatigue is unfortunately widespread, and to a degree that can affect relationships, work capacity and overall well-being.

Another common symptom is very heavy bleeding - The article here describes menorrhagia, heavy bleeding, and what you should pay attention to. 

---

Why do symptoms vary so much?

Because the spread of the disease in the body varies from person to person, and because hormone levels also play a role, the symptoms can also vary.

For example, if the tissue affects the intestines or bladder, something as ordinary as going to the toilet can become painful, and it can also block passage in, for example, the intestines, fallopian tubes, etc. 

In others, the disease manifests itself primarily as extreme menstrual pain.

Because the symptoms can be so complex, it can be easier to just brush it off and write it off as “just bad periods,” even though the reality is much more nuanced. Minimizing it to “stomach ache” is definitely minimizing the discomfort and symptoms of endometriosis, and unfortunately, it is also much more complicated to treat than if it were “just” menstrual cramps.

Maybe you need a menstrual product that doesn't need to go into the body to reduce irritation to the uterus, and menstrual panties can really be a good alternative here. You can find the selection of menstrual panties here. 

---

Why does it take so long to be diagnosed with endometriosis?

Both patients and professionals lack knowledge. New research shows that less than two percent of women of childbearing age are diagnosed with endometriosis, even though it is estimated that the disease affects over five times as many - 1 in 10.

Many young, undiagnosed women with endometriosis may reach out to their doctor because they have severe menstrual pain. But instead of investigating the cause of the pain, they are sent home with painkillers or put on hormonal contraception. 

Hormonal contraception, such as birth control pills, can mask the symptoms of endometriosis because the form of contraception regulates the hormones, which are also the ones that affect the activity of endometriosis. And this can mean that you actually end up masking the symptoms so that you go even longer without discovering that you actually have endometriosis. And this is a big challenge, since endometriosis can also cause infertility. If you stop taking hormonal contraception when you want to be pregnant one day, you may have significantly more difficulty getting pregnant. 

Although endometriosis is not a new disease, it often takes many years to be diagnosed. On average, between five and seven years, from the time a person first seeks medical attention with symptoms until the diagnosis is finally made.

And it's not because patients don't seek help. On the contrary, research shows that people with endometriosis often have frequent contact with the healthcare system up to ten years before diagnosis.

Yet the disease often goes under the radar - unfortunately also due to medical bias and ignorance. 

---

How is endometriosis treated?

There is no cure for endometriosis yet, but there are several treatment options that can help relieve symptoms. Treatment depends on symptoms, age, and whether you want to get pregnant.

Typical treatments may include:

Pain relief
For example, painkillers that can reduce inflammation and pain.

Hormone therapy
Hormone therapy can dampen the body's hormonal cycle and thus reduce the activity of the endometriosis tissue. This can include hormonal spirals, birth control pills or other hormonal preparations. When we talk about hormonal contraception, then you should read the article about doctor and researcher Amani Meadi's research project Safe Choice.

Operation
In some cases, doctors may attempt to remove endometriosis tissue through surgery. This may provide symptom relief, but unfortunately it does not eliminate the disease, so symptoms and discomfort may return.

For many, treatment at this time is therefore about to find a way to live with the diseasewhere pain and symptoms become as manageable as possible.

---

What happens to endometriosis during menopause?

Because endometriosis is closely linked to the body's hormones – especially estrogen – many people find that the symptoms decreases after menopause.

When menstruation stops, estrogen levels in the body drop, which often means that the endometriosis tissue is no longer stimulated in the same way as before. For some, the pain may therefore decrease over time.

But that doesn't necessarily mean that the disease will completely disappear.

In some people, endometriosis can still cause symptoms after menopause, especially if there is still active tissue in the body. This also applies to people who receive hormone therapy in connection with menopause, because in some cases the hormones can affect the disease.

In short: Many people experience an improvement after menopause – but endometriosis can still exist in the body.

👉 Read the article about how to spot the symptoms of perimenopause.

---

Adenomyosis – a closely related disease

When talking about endometriosis, it is important to also mention adenomyosis, which endometriosis is often confused with because the diseases are similar.

In adenomyosis, tissue that resembles the uterine lining grows into the muscle wall of the uterus itself. This is what happens inside the uterus, while endometriosis is typically found outside the uterus.

Adenomyosis can cause, among other things:

• very heavy menstrual bleeding

• severe menstrual pain

• an enlarged or tender uterus

Some people have both endometriosis and adenomyosis at the same time. 
As with endometriosis, symptoms can often subside after menopause because the disease is also hormone-dependent.

👉 Curious about other hormonal imbalances, read the article here.

---

We have known about endometriosis for thousands of years

With the increasing focus on endometriosis in society, it may seem like a new disease we have discovered. However, endometriosis was actually officially named in 1920, and the symptoms of the disease have been described much earlier.

In the Hippocratic writings Hippocratic Corpus, written around the 5th and 4th centuries BC, there are descriptions of pain and symptoms that are strikingly similar to what we associate with endometriosis today.

In the big picture, however, the disease is still surprisingly unknown, even though both patients and organizations are doing an immense amount of work to spread awareness and influence political initiatives that can improve the conditions for investigation and research into the diagnosis.

---

Why is endometriosis still an overlooked disease?

The simplified and also sad explanation is probably that endometriosis primarily affects women.

For thousands of years, medical research has centered around men because women's bodies are complicated, because they have a cycle of hormonal changes and fluctuations - and that makes research more complicated, lengthy and expensive - roughly speaking, it's much easier if you just focus on the male body, which has few hormonal fluctuations. 

That approach has actually been so formalized and openly acceptable in research that it had a concept: “the reference man”. The archetype on which all our research, including medical trials, symptom pictures and treatment, is based: A white man between 20 and 30 years old, weighing around 70 kilos and 180 centimeters tall.

The structure and history are also called medical biasThe male body has been the default - the female body the anomaly.

The consequence of medical bias, which also negatively affects people of other ethnicities, ages, etc., is that diseases that primarily affect women have historically received less attention in research and treatment.

Endometriosis is a clear example.

In the United States, where the disease among women is almost as prevalent as type 2 diabetes, the American National Institute of Health annually only a few dollars on endometriosis research per patient.

In comparison, the organization uses around 30 dollars per diabetes patient.

But it's not just women-related diseases that are overlooked - when symptom patterns, medical research and development, and treatment plans are designed based on a male body, many diseases in women are overlooked because they can appear differently in a female body than in a male.

For example, this has the consequence that even though we know, that 70% of patients with chronic pain are women, then 80% of studies on chronic pain are based on men. We know that more women die from cardiovascular disease because the symptoms we think we should be looking for are actually men's symptoms. This means that women with ADHD are diagnosed significantly later, with mental health problems as a consequence. That women can experience significantly more side effects from medication than men do. 

We can see this pattern repeated in an incredible number of places in research, and the consequence is that even though women live longer than men, they have significantly more years of illness and lower well-being than men. And another sad fact about the bias: Male doctors who have daughters provide better treatment to women than men without daughters, and this has such an impact that women have a greater chance of surviving on the operating table, for example, if the male doctor has daughters. 

It is a major structural problem that requires a confrontation and political action - which is why it was decided in 2025 that Denmark should have a national research center for women-related diseases, to pool research and ensure faster dissemination of new knowledge.

---

Endometriosis is not just a women's problem – but a societal problem

Endometriosis doesn't just affect the individual. An international study from 2011 showed that on average, people with endometriosis lose around 11 working hours per week due to the disease. It can therefore also have a financial cost for the individual. 

When so many people have to go to bed every month with pain that can be so severe that in some cases it forces them out of the labor market, it has consequences far beyond the individual.

It affects work life, family life and social life.

In short: It's not just a women's problem. It's a societal problem. It's a workforce problem. It's a well-being problem and a family problem (even when it ends up causing infertility).

---

More attention to endometriosis in Denmark

But it's changing! The attention, the publicity and the knowledge in the field. 

In Denmark, funds were allocated in the 2024 Finance Act to raise awareness about the disease. The amount was modest – 100,000 kroner – but the symbolic value was great:

For the first time, endometriosis was recognized as a national issue requiring political attention. 

A small step. But an important one for a large patient group that has been overlooked for many years.

---

We would like to end with a really important point:

We need to stop training girls to accept pain as a "natural" part of life - we do this when we dismiss, reject, and don't listen when they express pain.

Menstrual cramps are not "completely normal". Menstrual cramps are widespread, yes, but it is not normally. When something is normal, it is also acceptable, and we should not do anything about it. 

But menstruation shouldn't be painful. It can be grumbling, it can be slightly uncomfortable to have menstruation, also because your sleep quality can be affected hormonally, because the uterine cramps caused by prostaglandins, among other things, can also cause diarrhea, etc. But we shouldn't grow up believing that this is what it's like to be a woman. It should be painful and suffering.

This attitude causes us to ignore the body's signals, symptoms, diseases (like endometriosis) and potentially also cross boundaries. We are ready to confront that. 

Facts about endometriosis

• Endometriosis affects an estimated 190 million people globally

• Around 130,000 Danes living with the disease

• The disease is most often found in the pelvic area.

• However, endometriosis tissue is also found in, among other things: intestines, bladder, lungs, kidneys and in rare cases the heart

• In very rare cases, the disease has also been observed in men.

FAQ: Endometriose

Why do people get endometriosis?

Scientists still don't know exactly why some people develop endometriosis. Several theories try to explain the disease. One of the most well-known is called retrograde menstruation, where menstrual blood flows backwards through the fallopian tubes and into the abdominal cavity.
Other researchers point to genetic factors, the role of the immune system, hormonal influences, developmental disorders already in the fetal stage.

It is likely a combination of several factors.

How is endometriosis diagnosed?

Due to historical reasons, lack of research, and other factors, endometriosis can be difficult to diagnose. The diagnosis is typically made through a combination of a discussion about symptoms, a gynecological examination, and scans (ultrasound or MRI).

In some cases, it requires a laparoscopy to make the diagnosis with certainty.

Who can get endometriosis?

Endometriosis typically affects people of childbearing age. Symptoms can begin as early as the teenage years, but the diagnosis is often not made until many years later.

The disease occurs primarily in people with a uterus, but rare cases are also found in men.

Can endometriosis be cured?

There is no cure for endometriosis yet. Treatment typically involves relieving symptoms through medication, hormone therapy, or in some cases surgery.

Are severe menstrual cramps normal?

Many people experience pain during menstruation, but pain that is so severe that it prevents you from going to school, working, or living normally should always be investigated.

Can you have endometriosis without knowing it?

Yes. When only about 2% of all people with endometriosis have the diagnosis, but we expect that 10% of women of childbearing age suffer from it, there is unfortunately a large backlog in the investigations.  

Sources:

• "Study reveals major underdiagnosis of widespread female disease" - Aarhus University (source)
• Finance Act (source)
• "Women and pain: Disparities in experience and treatment" - Harvard University (kilde)
• "Impact of endometriosis on quality of life and work productivity: a multicenter study across ten countries" - Nnoaham KE, Hummelshoj L, Webster P, d'Hooghe T, de Cicco Nardone F, de Cicco Nardone C, Jenkinson C, Kennedy SH, Zondervan KT; World Endometriosis Research Foundation Global Study of Women's Health consortium (kilde)