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Endometriosis Explained: What It Is, Causes, Symptoms, Types, and Stages
Endometriosis affects an estimated 1 in 10 people during their reproductive years, yet it remains one of the most misunderstood, misdiagnosed, and under-researched conditions in women's health. The average person with endometriosis waits up to seven years to receive a diagnosis. Endometriosis is one of the most common causes of heavy painful periods, pelvic pain, pain with intercourse (dyspareunia) and can lead to fertility issues.
What Is Endometriosis?
Endometriosis is a condition in which cells similar to, but not identical to, the lining of the uterus (called the endometrium) grow outside of the uterus. These growths, called lesions or implants, most commonly develop on the ligaments of the uterus, pelvic side walls, ovaries, and fallopian tubes, though they can appear almost anywhere in the body.
Unlike the uterine lining, which sheds during a menstrual cycle, endometriosis lesions have no way to exit the body. Instead, they release inflammatory factors that cause pain, scarring, and adhesions in the surrounding tissue. This is what makes endometriosis both progressive and painful.
An important distinction: endometriosis is not the same as adenomyosis, though the two conditions frequently co-exist. Adenomyosis occurs when similar tissue grows into the muscular wall of the uterus itself and is a common source of cramping pain in people who also have endometriosis.
One more thing worth knowing: researchers believe many people are born with the predisposition to develop endometriosis. The condition has been identified in fetuses, and lesions have been found in locations entirely outside the pelvis, suggesting the disease is far more complex than a simple menstrual backflow.
What Causes Endometriosis?
The exact cause of endometriosis is not yet known. This is not for lack of importance; it reflects decades of underfunded research into a condition that disproportionately affects women and people assigned female at birth. Emerging science, including research into the epigenetic roots of endometriosis, is beginning to change that picture.
Several working theories are currently supported by evidence:
Retrograde menstruation is the most widely cited theory. It proposes that menstrual blood containing endometrial cells flows backward through the fallopian tubes and into the pelvic cavity, where some cells implant and begin to grow. However, retrograde menstruation occurs in many people who never develop endometriosis, which suggests this alone does not explain the condition.
Cellular metaplasia suggests that cells outside the uterus spontaneously transform into endometrial-like cells and then spread through blood or lymphatic vessels. This theory could explain why endometriosis lesions are occasionally found far from the pelvis, including in the lungs and brain.
Genetic predisposition plays a measurable role. People are significantly more likely to develop endometriosis if a first-degree relative, such as a mother or sister, has the condition. Twin studies further support a heritable component.
Immune system dysfunction is another key factor. A healthy immune system would typically identify and destroy endometrial tissue growing in the wrong location. In people with endometriosis, that response appears compromised, allowing lesions to establish and grow.
Epigenetic factors represent a cutting-edge area of research. Epigenetics refers to changes in gene expression that do not alter the underlying DNA sequence but can dramatically affect how genes behave. Tia has covered this emerging research in depth, exploring how epigenetic mechanisms may help explain why endometriosis develops, why it varies so much between individuals, and why it may begin before birth. Read the full research article here.
What Are the Symptoms of Endometriosis?
The hallmark symptom of endometriosis is pelvic pain, most commonly associated with menstrual periods. But defining endometriosis by period pain alone is one reason it takes so long to diagnose. The symptom profile is wide, inconsistent, and frequently overlaps with other conditions.
The most common endometriosis symptoms include:
- Pelvic pain that is significantly worse than typical period cramps
- Pain during or after sexual intercourse (dyspareunia)
- Painful bowel movements or urination, especially during menstruation
- Heavy menstrual bleeding or bleeding between periods
- Bloating, which some refer to as "endo belly"
- Nausea, constipation, or diarrhea, particularly around the menstrual cycle
- Chronic fatigue
- Anxiety and depression
- Infertility or difficulty conceiving
Why endometriosis symptoms are misleading:
One of the most critical things to understand is that the severity of symptoms does not reliably reflect the extent of the disease. Someone with stage 1 (minimal) endometriosis may experience debilitating pain, while someone with stage 4 (severe) endometriosis may report only mild discomfort. This disconnect is a major reason why endometriosis is so often dismissed or minimized by both patients and clinicians.
How Endometriosis Is Diagnosed
Because so many endometriosis symptoms overlap with other conditions, it is commonly mistaken for irritable bowel syndrome (IBS), pelvic inflammatory disease (PID), ovarian cysts, or even anxiety. Patients are often told their pain is "normal" or psychological.
The only definitive way to diagnose endometriosis is through laparoscopy, a minimally invasive surgical procedure performed under general anesthesia in which a surgeon uses a small camera inserted into the abdomen to directly visualize lesions. During the same procedure, a surgeon can also remove lesions and scar tissue, making laparoscopy both a diagnostic and potentially therapeutic tool.
Short of surgical confirmation, providers may reach a clinical diagnosis of "suspected endometriosis" based on symptom history, pelvic exam findings, and imaging. This approach allows treatment to begin without surgery, which is appropriate for many patients.
Research shows the average time from symptom onset to diagnosis is seven years. Advocating for yourself during that journey matters. Tracking your symptoms over time, including when they occur, what they feel like, and what makes them better or worse, gives your provider the clearest possible picture of your experience.
Types of Endometriosis
Endometriosis is not a single, uniform disease. It presents in distinct forms depending on where lesions develop and how deeply they penetrate tissue.
Superficial peritoneal endometriosis is the most common type. Lesions are shallow and located on the peritoneum, the thin membrane that lines the pelvic cavity. This corresponds to stage 1 or stage 2 disease.
Ovarian endometriomas (chocolate cysts) develop when endometrial tissue implants on the ovaries. As the tissue sheds and bleeds cyclically with no outlet, old blood accumulates within a cyst. These cysts are called "chocolate cysts" because of the dark brown color of their contents. Endometriomas are characteristic of stage 3 disease.
Deep infiltrating endometriosis (DIE) is the most severe form, in which lesions penetrate more than 5 millimeters into surrounding tissue. DIE can involve the rectum, bladder, ureters, and other pelvic structures. It is associated with the most significant pain and the greatest risk of organ dysfunction.
Extraperitoneal endometriosis is rare but serious. Lesions are found outside the pelvic cavity entirely, in locations such as the diaphragm, lungs, or even the brain. This form is often linked to the cellular metaplasia theory of origin.
The Four Stages of Endometriosis
The American Society of Reproductive Medicine (ASRM) staging system is the most widely used framework for classifying endometriosis. Staging is based on the number, size, depth, and location of lesions, as well as the presence of adhesions and ovarian cysts. It is critical to understand that this system was designed to predict fertility outcomes, not to measure pain or overall symptom burden.
Stage 1 Endometriosis: Minimal
Stage 1 involves small, shallow lesions with little to no scar tissue. Because these implants sit close to the surface of tissue (called superficial peritoneal endometriosis), symptoms can be light and the condition often goes undetected. Stage 1 endometriosis does not mean the condition is not affecting your life.
Stage 2 Endometriosis: Mild
Stage 2 involves more lesions and deeper implants than stage 1. While scar tissue may be present, significant inflammation is less common at this stage. Pelvic pain, especially during menstruation, becomes more noticeable. Pain during sex may also begin to emerge.
Stage 3 Endometriosis: Moderate
Stage 3 involves multiple deep implants and typically includes at least one ovarian endometrioma (chocolate cyst). Adhesions, bands of scar tissue that can cause organs to stick together, are also a feature of this stage. Symptoms at this stage tend to be more intense, may include heavy menstrual bleeding, and often begin to affect fertility.
Stage 4 Endometriosis: Severe
Stage 4 is the most advanced form of the disease. It involves extensive deep implants, large ovarian endometriomas, and widespread adhesions that can affect multiple organs within and potentially beyond the pelvis. Bowel, bladder, and fertility complications are common at this stage, and pain can be significant and constant.
A reminder about staging: The stage of endometriosis does not predict how much pain you will experience. Someone with stage 1 disease may suffer more than someone with stage 4, and that experience is just as valid and deserving of care.
How Endometriosis Is Treated
There are multiple treatment options available for endometriosis, ranging from pain management and hormonal therapies to minimally invasive procedures and fertility support.
Endometriosis Care at Tia
At Tia, our clinical team offers dedicated endometriosis appointments to help treat symptoms of endometriosis and provide personalized care plans. If you’re experiencing symptoms, schedule an appointment to explore your treatment options and get the support you deserve.
Endometriosis FAQs
How does endometriosis affect fertility?
Endometriosis is one of the leading contributors to infertility, accounting for a significant proportion of cases among people who struggle to conceive. It affects fertility through several interconnected mechanisms.
Inflammation and scarring in the pelvis can block or distort the fallopian tubes, preventing eggs from traveling to the uterus for fertilization. Endometriomas on the ovaries can compromise ovarian reserve, reducing the number and quality of available eggs. The inflammatory environment associated with endometriosis can also affect sperm function and reduce the receptivity of the uterine lining to implantation.
Hormonal imbalances, particularly elevated estrogen levels, are another factor. Estrogen is the primary driver of endometriosis growth, and an estrogen-dominant environment can disrupt ovulation and menstrual cycle regularity.
It is important to know that many people with endometriosis do conceive, sometimes naturally and sometimes with support. Fertility is not a foregone conclusion in any direction. Speaking with a provider who understands both endometriosis and reproductive medicine is the most important step.
Is there a connection between endometriosis and PCOS?
Endometriosis and polycystic ovary syndrome (PCOS) are separate conditions with different causes. However, research suggests that a significant number of people with one condition also have the other. Shared contributing factors, including systemic inflammation, high androgen levels, and insulin dysregulation, may help explain the overlap. If you have been diagnosed with one, it is worth asking your provider to assess for the other.
Can you prevent endometriosis?
There is currently no known way to prevent endometriosis. However, because estrogen appears to drive the growth of endometriosis lesions, some strategies aimed at reducing estrogen levels may lower risk or slow progression. These include regular physical activity, maintaining a healthy body composition, limiting alcohol and caffeine, reducing consumption of red and processed meat, and eating a diet rich in fiber and anti-inflammatory fats such as omega-3 fatty acids from fatty fish, nuts, and seeds.
Some people with endometriosis also report symptom improvement on a gluten-free, dairy-free, or low-FODMAP diet. These approaches are not universally effective, but they are low-risk to try and worth discussing with your provider.
What are ways you can test for endometriosis?
There’s currently no diagnostic test for endometriosis. Instead, a healthcare provider will use your medical history, symptoms, pelvic exam findings, and clinical suspicion to diagnose the condition.
The only way to definitively diagnose endometriosis is through laparoscopy. A laparoscopy is a minimally invasive procedure done under general anesthesia that allows a surgeon to visualize endometriosis with a small camera inserted into the abdomen.
During the procedure, a surgeon can also remove endometriosis lesions and scar tissue found in the pelvic cavity, which also makes laparoscopy one of the most effective treatment options.
How can you advocate for yourself when you've been misdiagnosed and know there's something more serious going on?
Though endometriosis affects up to 10% of women of reproductive age, it remains a mysterious and misunderstood condition to many in the medical field. Research shows it can take up to seven years for someone with endometriosis to receive a diagnosis, which is why it’s essential to become an advocate for yourself and your healthcare. Here are a few tips to help you be seen and heard on your journey to find relief from endometriosis symptoms:
- Find the right physician: Research endometriosis experts in your area and get recommendations from family members and friends who have firsthand experience with endometriosis and clinical experts who treat it.
- Study up: Educate yourself about the disease and stay up-to-date on the most recent research and treatment options. Be familiar with the landscape, language, and challenges people have faced in their search for answers about endometriosis.
- Get prepared: Keep track of your symptoms (there are apps that can help!) and make sure you have answers to questions your provider will ask: When did your symptoms start? How often do they occur? Where is the pain and what does it feel like? Does anything make it better or worse?
- Have your history ready: Bring recent medical records with you and practice giving your history in a clear, concise way.
- Bring someone with you: Ask a family member or friend whom you trust to come with you to your appointment. Have a list of questions ready and ask this person to take notes so you can concentrate on telling your story and listening to responses.
- Be assertive and inquisitive: Speak up, don’t downplay your pain, and make sure you communicate how your symptoms impact your life, including your work, relationships, and daily activities. If you’re feeling dismissed, consider posing your concerns as questions: My sister got relief from laparoscopy, can we talk about what that looks like for me? I’m nervous about birth control, can we talk about other options?
- Stay focused: Keep your visit focused on endometriosis symptoms, unless your provider asks about unrelated issues. Do your part to make the appointment as efficient and effective as possible. Doctors are busy, but so are you. Mutual respect for each other’s time can go a long way.
- Trust your gut: If the visit feels rushed or something feels off, get a second opinion. Or a third one. Don’t stop seeking support until you and your symptoms are taken seriously.
How can I use diet to combat the symptoms of endometriosis?
Inflammation and high estrogen levels can make endometriosis symptoms worse, and your eating habits can impact both factors. While there isn't a cure-all endometriosis diet we can recommend, there are several diet guidelines one can follow.
Eating more fiber and less fat can reduce estrogen levels and improve symptoms. Also, adding omega-3 fats (from fatty fish, nuts, seeds, and plant oils) and monounsaturated fats (like avocados and olive oil) can help ease inflammation. Certain foods and drinks can make symptoms worse by increasing inflammation and estrogen levels. These include meat, processed foods, alcohol, caffeine, and sugary drinks.
Some people with endometriosis feel better on a gluten-free or dairy-free diet as well. A low-FODMAP diet, designed for people with IBS (irritable bowel syndrome), has shown promise in treating endometriosis symptoms too.
Is there any connection, direct or indirect, between endometriosis and PCOS?
Endometriosis and PCOS are separate conditions with different causes. However, recent studies indicate that a significant number of people with PCOS also have endometriosis, and vice-versa. So, yes, women with endometriosis seem to have an increased risk of having PCOS. And clinical experts should be aware of the potential for these conditions to co-exist.
Research is limited but suggests that contributing factors affecting both conditions—like inflammation, high androgen levels, and high insulin levels—might explain the connection.
What are your thoughts on using hormonal birth control to control the growth of endometriosis tissue?
Hormonal birth control, including combined therapy (estrogen and progestin) and progestin-only options, is considered the first-line treatment of choice for endometriosis. Although a recent study found that progestin-only pills may be a better treatment for endometriosis than combined estrogen-progestin therapy, probably because estrogen can worsen symptoms of endometriosis.
These medications reduce hormones that regulate ovulation and periods and thin the lining of the uterus, which can improve endometriosis-related pain and prevent the condition from getting worse. Your provider will be able to discuss benefits, drawbacks, and options with you.
Is it necessary to get an endometriosis diagnosis? Since there’s no cure, should I just treat myself as if I have it?
There’s little harm in using home remedies like heat, over-the-counter pain relievers, and anti-inflammatory foods to treat endometriosis symptoms. However, it’s still recommended to make an appointment with a healthcare provider to undergo an exam and discuss your symptoms before going at it alone. Since endometriosis shares symptoms with several other medical conditions, your provider will be able rule out other conditions and recommend the most effective treatment plan, which may include prescription medication or surgery.
Are there ways to prevent endometriosis?
You can’t prevent endometriosis, but you may be able to reduce your chances of developing it by lowering estrogen levels. Taking hormonal birth control; getting regular exercise; maintaining a low percentage of body fat; limiting consumption of meat, alcohol, caffeine, and sugary drinks; and eating a diet high in fiber and healthy fats are all strategies that might help achieve this goal.
At Tia, we understand the complexities and challenges associated with managing endometriosis, and the impacts it has on both your physical body and your emotional well-being. That's why we've developed a comprehensive, holistic approach to provide our patients with the support and care they need . Wherever you are on your journey, we're here to provide the support and resources you need to live your fullest life.