Endometriosis Symptoms & Stages: What Each Stage Means

If your periods have always felt harder than everyone else's, you're not imagining it. Endometriosis affects 1 in 10 women of reproductive age*, yet getting answers can take years, partly because symptoms, such as severe pain, are often dismissed as ordinary period pains and something that should be quietly endured.

Here we explain the most common endometriosis symptoms, what stages 1 to 4 mean, and why the endometriosis stage does not reliably predict how much pain you’ll experience. 

*Endometriosis UK. (2026). What is Endometriosis? 

What Is Endometriosis?

Endometriosis is a long-term condition in which tissues similar to the womb lining grow elsewhere in the body. It commonly affects the ovaries, fallopian tubes and tissue lining the pelvis, but it can also affect other organs including the bowel and bladder. The cells respond to hormonal changes, causing inflammation, pain, and scar tissue; if endometriosis affects your ovaries, it can form cysts known as endometriomas, while bands of scar tissue, called adhesions, can cause organs to “stick” together.

Endometriosis can have a significant impact on your physical health, relationships, work, education, and emotional wellbeing. Yet help is available, and effective ways to manage your symptoms exist.

What Are the First Signs of Endometriosis?

Often, the earliest sign of endometriosis is pelvic pain or cramping that feels far beyond an ordinary cramp. You might miss work or school, cancel plans, struggle to sleep, or find that standard painkillers simply do not cut it and provide little, if any, relief. Pain or cramping that regularly stops you from living your usual life shouldn’t be waved away as “just a period”.

However, one of the most common initial signs of endometriosis is being told your symptoms are normal and to be expected. Because symptoms can begin in adolescence or during your 20s, being told that your symptoms are typical of the menstrual cycle or just a natural part of being a woman is not proof that nothing is wrong. It’s also a very common occurrence and is one of the key reasons why it can take, on average, 9 years and 4 months to receive an endometriosis diagnosis in the UK*.  

Many early signs of endometriosis are subtle and less noticeable than the more common symptoms. They can include:

• Lingering pain after a period – prolonged pain after a period and not just during it can be an early sign of endometriosis

• Heavy bleeding – unpredictable menstrual cycles, difficulty getting pregnant, and heavy bleeding 

• Painful sex – pain or cramping during or after sex

• Digestive discomfort – bloating, feeling sick, constipation, diarrhoea, and painful bowel movements

• Fatigue – feeling tired or exhausted, especially if it doesn’t match your activity levels

• Urinary symptoms around your period – pain when passing urine, or blood in your urine, that follows your cycle

*Endometriosis UK. (2026). Endometriosis UK release new report highlighting alarming increase in endometriosis diagnosis times. 

Common Endometriosis Symptoms

Common endometriosis symptoms can vary from person to person. You may get symptoms that mainly occur around your period, during other key moments in your cycle, or throughout the month. If any of the following symptoms feel familiar, reach out to your Hers clinician.

Common endometriosis symptoms include:

• Severe period pain that interrupts your daily life 

• Heavy periods that cause you to bleed through your clothes or require you to change a pad or tampon every 1 to 2 hours

• Pain in your lower stomach or back

• Pain during or after sex

• Painful bowel movements or when passing urine, which may be worse during your period

• Bloating, sometimes called “endo belly”

• Feeling sick, constipation, or diarrhoea

• Constant or cyclical fatigue

• Infertility or difficulty getting pregnant

Some people experience several symptoms, while others may only get one or two. It’s also possible to have no symptoms at all, and the first indication that they may have endometriosis is when they find it difficult to conceive. 

How your symptoms feel, or how severe they are, doesn’t reveal the true extent of the condition. In the same way, the number of symptoms or your pain level cannot be used to determine which stage of endometriosis you are at. 

One of the best ways to support a diagnosis and get appropriate treatment is to keep a symptom diary. Record when you feel pain or when you bleed, how it affects your daily routine, and whether unusual or uncomfortable bowel, bladder, or digestive symptoms follow your menstrual cycle. This can help your clinician see patterns you might otherwise miss.

The 4 Stages of Endometriosis

The revised American Society for Reproductive Medicine (rASRM) divides endometriosis into 4 stages: minimal, mild, moderate and severe. These stages describe what is found during surgery, including the location and extent of endometriosis, and usually cannot be determined by symptoms alone. 

How is endometriosis diagnosed before it is staged?

Under updated NICE guidance, your doctor will offer you a transvaginal ultrasound if they think you may have endometriosis, even if abdominal or pelvic examination is normal.* This internal scan can help identify ovarian endometriomas, deep endometriosis and other conditions that could be causing your symptoms. It can also help determine whether you need a referral to a gynaecologist. 

If a transvaginal ultrasound is unsuitable for you or you would prefer not to have one, a transabdominal pelvic ultrasound may be considered instead. However, a normal ultrasound does not rule out endometriosis. You may still need a referral for further assessment, which could include a specialist ultrasound, an MRI scan or a laparoscopy.

During a procedure where a small camera is passed through a small cut in your stomach, called a laparoscopy, a surgeon can assign points based on the location, size, and depth of visible endometriosis, whether you have ovarian endometriomas, and the extent of any adhesions to help determine your stage.

Source: Obstetrics and Gynaecology. (2012). The rASRM score and the Enzian classification for endometriosis: their strengths and weaknesses. 

These descriptions are relatively broad, and endometriosis does not always neatly progress from one stage to the next. The system also doesn’t explain every form of the condition, and there are other systems that can be used to record more severe or deep endometriosis or estimate fertility outcomes.

* NICE. (2024). Endometriosis: diagnosis and management.

Endometriosis Stage Doesn't Equal Symptom Severity

If you have stage 1 endometriosis, your pain can impact every aspect of your daily life. If you have stage 4, you might have almost no symptoms at all, and only discover you have it during fertility investigations or surgery. 

The rASRM system measures what a surgeon can see –  lesions, endometriomas and adhesions – but it doesn’t measure your nerve involvement, your inflammation, your pain sensitivity or the effect symptoms have on your daily life. 

That is why NICE recommends offering treatment based on your symptoms, preferences and priorities rather than your stage of endometriosis*.

Stage may still give clinicians useful anatomical information. For example, adhesions or endometriomas can affect fertility by changing how the ovaries and fallopian tubes function. However, stage alone cannot predict whether someone will have fertility difficulties. Many people with endometriosis become pregnant naturally, while others may need specialist support.

Your pain does not have to match a scan, surgical finding or numbered stage to be legitimate.

*NICE. (2024). Endometriosis: diagnosis and management. NICE guideline NG73.

What Causes Endometriosis?

One of the most frustrating things about endometriosis is that the exact cause is unknown, which can leave you wondering “why me?” However, we do know it likely results from a combination of biological and genetic factors rather than a single process or cause.

Some of the proposed explanations include:

Retrograde menstruation

During a period, some of your womb lining flows backwards through the fallopian tubes and into the stomach area (abdomen) and pelvis. This tissue can implant itself into the organs in the pelvis and grow. It’s thought that most people who have periods experience some form of retrograde menstruation*, but their body is able to clear the tissue before it attaches elsewhere in the body. For this reason, retrograde menstruation doesn’t clearly explain why some people develop endometriosis, and others do not. 

*NHS. (2024). Endometriosis.

Your genes

Sometimes endometriosis runs in families, suggesting some genes are passed down to new generations and contribute to the condition. Recent research has identified 80 areas in the genome where genetic variants can increase the risk of endometriosis*, which could offer new insights for future diagnosis and treatment. 

*Nature Genetics. (2026). Multi-ancestry genome-wide association and integrated multi-omics analyses of endometriosis and its clinical manifestations. 

Cells moving through blood or lymph

It’s believed that endometriosis cells can travel to other areas of the body through the bloodstream or lymphatic system, which may explain why it has been found in the brain, eyes and diaphragm.*

*Burney RO et al. (2012). Pathogenesis and Pathophysiology of Endometriosis.

Immune system differences

The immune system may not recognise or clear misplaced endometriosis cells, and several immune cells have been identified in the condition's development*. However, it is unclear whether the immune system causes endometriosis or whether its dysfunction results from it. 

*Cells. (2022). The Role of the Immune System in the Development of Endometriosis. 

Environmental factors

Chemicals and air pollution are some of the potential environmental causes of endometriosis. These can alter hormone levels, cause inflammation and result in oxidative stress. Animal studies have found that exposure to dioxin, a type of toxic industrial pollutant, can cause endometriosis and impact its severity*. However, this is yet to be confirmed in humans.

When it comes to understanding the cause of endometriosis, these are just theories that offer some explanation. One or more of these factors, or none, may have caused your symptoms. Rest assured, endometriosis is not caused by anything you have eaten, done, or failed to do. 

*Environmental Health Perspectives. (2002). Dioxins and endometriosis: a plausible hypothesis.

Who Can Get Endometriosis?

Anyone who gets periods can get endometriosis, and it is most likely to occur between puberty and menopause. Symptoms can start as early as your first period, but diagnosis is not likely to happen until much later in life – a frustrating reality for many women going through this.

There are several risk factors for getting endometriosis, although these do not guarantee that you will definitely get it:*

• Having a family member, such as a mother, sister, or daughter, who has the condition

• Starting your periods before the age of 11

• Having shorter menstrual cycles (less than 27 days)

• Heavy periods or menstrual bleeding

• Having a condition that obstructs normal menstrual blood flow

*NICE. (2025). Endometriosis: What are the risk factors?

Treatment Options

Unfortunately, there is no available treatment that can cure endometriosis, but there are treatments available that can help manage symptoms, including pain, and support your fertility journey. The right choice for you will depend on your symptoms, medical history, personal preferences and whether you are trying to become pregnant.

Some options may include:

• Painkillers – paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can be effective for managing pain in some people.

• Hormonal treatment – examples include the combined contraceptive pill, progestogen-only treatment or a hormonal intrauterine device (IUD), like the coil, which can reduce or stop bleeding and ease pain.

• Surgery – if other treatments have been unsuccessful or you have lots of endometriosis, surgery may be a consideration to remove the tissue, target adhesions, or even remove your womb or ovaries, if appropriate. 

• Fertility support – you may be referred to a fertility specialist if your endometriosis is affecting your ability to get pregnant.

Mental health support – endometriosis can be a major burden on your mental wellbeing, so if it is affecting your mood or making you anxious, mental health support is a vital part of treatment.