What is Endometriosis?
Endometriosis affects an estimated 176 million women around the globe, causing many to suffer a life of pain and debilitation and sometimes infertility. It mostly affects women of childbearing age and usually disappears after menopause. Endometriosis is often a long-term condition, with no simple cure. But there are treatments which can help.
Understanding Endometriosis: A Common Yet Often Misunderstood Condition
Endometriosis is a common gynaecological condition, affecting an estimated 10% of women during their reproductive years. It is characterised by the presence of endometrium-like tissue outside the uterine cavity.
These ectopic cells respond to hormonal changes in the menstrual cycle, building up and shedding as the uterine lining does. However, without an outlet, this leads to inflammation, often causing significant pain—particularly before and during menstruation.
Who Gets Endometriosis?
Endometriosis can affect anyone with a uterus, but certain factors may increase the risk of developing the condition. Common risk factors include:
- Early onset of menstruation (getting your first period at a young age)
- Short menstrual cycles (typically less than 27 days)
- Heavy or prolonged menstrual flow
- Low body mass index (BMI)
- Family history of endometriosis (especially in a first-degree relative)
- Late onset of menopause
WHEN DOES ENDOMETRIOSIS DEVELOP?
Endometriosis is almost exclusively found in women who produce sufficient levels of the hormone oestrogen. Some young girls have painful periods, but it is unclear whether these are endometriosis related. Theories exist that connect the onset of endometriosis as far back as to the embryonic or perinatal period. It is unclear why endometriosis suddenly develops, over what time frame, and whether and in whom it gets worse, stays the same or potentially even gets better spontaneously.
Common symptoms of ENDOMETRIOSIS
Painful or heavy periods
Spotting between periods
Cyclical or constant abdominal and pelvic pain
Pain during sex
Pain when urinating or passing stools
Lower back pain
Fatigue
Bloating
Difficulty conceiving (infertility)
Less common symptoms
- Repeated lung collapses (pneumothorax)
- Bleeding from Caesarean section scars, the umbilicus, the bowel, bladder or other body openings
- Painful or bulging lumps
HOW DOES ENDOMETRIOSIS DEVELOP?
Although many theories exist it remains unclear how endometriosis develops. The ‘retrograde menstruation’ theory is the most accepted theory where endometrial tissue and cells enter the abdominal cavity through the Fallopian tubes at the time of the menstrual period.
Studies have demonstrated that endometriosis is also caused by over/under expression of biochemical factors, genetic factors, and/or external factors. These factors cause rapidly spreading of endometrial tissue, attached to the abdominal wall, and invasion into the deeper layers by forming blood vessels for growth. Increasing evidence suggests that an impaired immune system and inflammation also plays a central role in these processes.
Endometriosis most commonly grow in the following areas, with different appearances, shapes and colours:
- Ovaries
- Fallopian Tubes
- Uterus
- Ureters
- Bowels or Bladder
- Abdominal Wall
However, none of the existing hypotheses have been completely proven and many mechanisms still remain unclear. It is possible that different mechanisms account for different presentations of endometriosis.
The revised American Fertility Society and American Society of Reproductive Medicine staging system of endometriosis is based on a points system that takes into account location, extent and depth of disease in relation to pelvic structures.Beyond the Surface: Mapping and Grading Endometriosis
Endometriosis commonly affects pelvic organs such as the uterus, ovaries, and fallopian tubes, as well as anatomical structures including the ovarian fossae, uterosacral ligaments, rectovaginal septum, pouch of Douglas, and uterovesical fold.
Lesions vary in size—from tiny punctate spots to nodules several centimetres wide, and ovarian cysts (endometriomas) that can reach the size of grapefruits.
The revised American Society for Reproductive Medicine (rASRM) classification stages endometriosis from I to IV:
Stage I (minimal, 1–5 points): few superficial lesions or adhesions
Stage II (mild, 6–15 points): deeper peritoneal lesions, possibly with superficial lesions or filmy adhesions
Stage III (moderate, 16–40 points): typically includes an endometrioma and/or dense adhesions
Stage IV (severe, >40 points): bilateral endometriomas, extensive adhesions, and possible obliteration of the pelvic cavity
Crucially, the staging does not reliably reflect the severity or location of symptoms.
Is Endometriosis a genetic disease?
Twin studies have shown increased concordance for endometriosis in monozygotic (identical) twins compared to dizygotic (fraternal) twins with heritability estimated at 52%. Although endometriosis often clusters in families, it is not a single-gene (monogenic) disease that is caused solely by inheriting a rare genetic variant from parents. Instead, endometriosis is a common complex condition that is caused by a combination of multiple genetic and environmental factors. Some other examples of common complex conditions include asthma, hypertension and migraine.
We are conducting many studies to identify these multiple genetic variants with small effects that contribute to endometriosis susceptibility. Most common type of genetic variation in our genome is called single nucleotide polymorphisms (SNPs) that are single letter changes in our DNA.
We conduct genome-wide association studies (GWAS) that screen endometriosis cases as well as endometriosis free-individuals and compare whether individuals with endometriosis have SNPs that occur more or less commonly compared to endometriosis free-individuals. Identification of the SNPs that are associated with endometriosis enables us to understand the underlying genetic mechanisms that make some women more susceptible to this enigmatic condition.
Lesion Types and Their Characteristics in Endometriosis
The vast majority of endometriotic lesions are found in the female pelvis and can vary significantly in appearance, shape, and colour. They may be superficial or deeply invasive, affecting the abdominal lining (peritoneum) and organs such as the bowel, bladder, and ureters—two long tubes in the posterior pelvic side wall that transport urine from the kidneys to the bladder.
Lesions can appear red, blue, brown, white, or vascular, and may present as adhesions, small vesicles, spots of various sizes, or firm nodules. Some evidence suggests that red lesions may be more 'active', although the clinical significance of this remains uncertain.
Transvaginal ultrasonography with Doppler flow image of a left-sided endometrioma (panel a) with a typical unilocular ground-glass appearance and minimal vascularity. T1-weighted MRI scan of a female pelvis with bilateral endometrioma (arrows) behind the uterus (asterisk; panel b). Because of their close proximity, this constellation is often called ‘kissing ovaries’. MRI of the pelvis of another female patient with endometriosis (panel c).HOW TO DIAGNOSE ENDOMETRIOSIS?
The most reliable method for diagnosing endometriosis in the abdomen is laparoscopy (keyhole surgery). This minimally invasive procedure allows doctors to directly examine the pelvic organs and confirm the presence of endometriosis.
In many cases, treatment can be carried out during the same procedure. However, laparoscopy is still a surgical procedure and requires general anaesthesia.
SHOULD I BE TREATED AND IF SO HOW?
If you are experiencing symptoms associated with endometriosis, treatment is generally recommended.
Management strategies should be individualised and take into account your specific circumstances, including whether you are currently trying to conceive. Endometriosis is an oestrogen-dependent condition, and most medical treatments aim to suppress oestrogen levels. As such, hormonal therapies form the cornerstone of medical management. However, hormonal treatment is typically not suitable if you are actively trying to become pregnant.
Medical therapy may also include analgesics, and treatment often involves a combination of medications to manage pain effectively.
An alternative approach is surgical management, which is usually via laparoscopy (keyhole surgery), rather than laparotomy (open surgery). Where possible, treatment is carried out during the same procedure, either by excising, ablating, or vaporising endometriotic lesions. It is important that such surgical interventions are undertaken by clinicians with expertise in endometriosis treatment to ensure optimal outcomes.
Surgery is an invasive intervention. Therefore, in some cases, clinicians may recommend empirical medical treatment without prior surgical confirmation of the diagnosis. If symptoms improve significantly with medical therapy, this may support the diagnosis of endometriosis.
However, a lack of response does not necessarily exclude the condition. In such cases, treatment may be adjusted, surgical options reconsidered, or referral to a specialist in endometriosis or a related field may be appropriate.
ARE THERE STUDIES I CAN BE INVOLVED IN?
Are you interested in making a real difference for those living with endometriosis? We're leading vital research to better understand this condition, develop non-surgical diagnostic tools, and discover more effective treatments.
By taking part in one of our clinical studies, you can play a direct role in advancing science and improving lives. We regularly have research opportunities open to participants.
👉 Visit our Clinical Research Studies page to see how you can get involved today.
WHAT DO I DO IF I HAVE ENDOMETRIOSIS AND I AM TRYING TO BECOME PREGNANT?
If you have been diagnosed with endometriosis and are trying to conceive, there is still a good chance of achieving a successful pregnancy naturally. However, if you do have problems conceiving it may be helpful to consult a fertility specialist or an endometriosis specialist.
They can perform a comprehensive assessment of both partners, which may include investigations such as hormone and ovarian reserve blood tests, semen analysis, and imaging or procedures to check if the fallopian tubes are open and functioning properly.
Depending on the findings and individual circumstances (such as age, severity of endometriosis, and how long you’ve been trying) fertility treatment may be recommended.
Patient support and Information
Several organisations are dedicated to supporting individuals affected by endometriosis and chronic pain, offering trustworthy information, practical guidance, and emotional support.
Endometriosis UK provides a wide range of services, including local and online support groups across the UK. These groups offer a safe and supportive environment where individuals can share experiences, connect with others, and access valuable information and resources.
👉 Click here to find a support group near you
In addition to support groups, Endometriosis UK runs a free helpline offering advice and emotional support:
📞 0808 808 2227
Endometriosis UK also hosts a welcoming online community, where thousands of people share their experiences and support one another.
👉 Join the online community
Related patient pages
What are Fibroids?
Fibroids are non-cancerous growths that develop in or around the womb (uterus). The growths are made up of muscle and fibrous tissue, and vary in size. They're sometimes known as uterine myomas or leiomyomas. Many women are unaware they have fibroids because they don't have any symptoms.
FENOX research study
FENOX is a prospective study that aims to improve our understanding of the underlying mechanisms of endometriosis and uterine fibroids and their associated symptoms by means of longitudinal observation and laboratory analyses.
Other WRH research projects
WRH comprises over 30 cutting-edge research groups spanning five core themes, each led by world-renowned experts in their respective fields. Many of these groups collaborate with other departments at the University of Oxford, as well as with universities and business partners globally.
Other useful links
- British Medical Journal Best Practice guidance on endometriosis
- Bupa information on endometriosis
- Endometriosis Association
- Endometriosis Information Leaflet
- International Pelvic Pain Society
- National Institute for Health and Care Excellence (NICE) guidance on the management of endometriosis
- NHS information on diagnosing and treating endometriosis
- Royal College of Obstetricians and Gynaecologists
- The Endometriosis and Fertility Clinic
- World Endometriosis Research Foundation
- World Endometriosis Society
How you can help
To help maximise the impact of the endometriosis research, we rely on the generous support of donors like you.
Your contribution is vital in advancing this research and driving meaningful discoveries.
