Endometriosis is a chronic inflammatory condition in which tissue resembling the endometrium occurs outside the uterine cavity and is associated with inflammation, pain and, in some people, infertility. The ectopic tissue can occur on pelvic structures such as the ovaries, peritoneum and tissues around the reproductive organs, although disease can occur in less common locations.
The condition is oestrogen-responsive and can undergo cyclical changes, but its biology is more complex than the simple idea that menstrual tissue has merely “travelled backwards”. Lesions can provoke inflammatory responses, fibrosis, adhesions and altered nerve signalling. Symptoms vary widely: some people have severe pain with relatively limited visible disease, while others have extensive anatomical disease with fewer symptoms. Endometriosis is therefore a heterogeneous disorder rather than a condition whose severity can be inferred from pain alone or from lesion size alone.
The origin of Endometriosis remains an area of active research. Retrograde menstruation, in which menstrual material passes through the fallopian tubes into the pelvic cavity, occurs commonly and may contribute to lesion formation, but retrograde menstruation alone cannot explain why only some people develop clinically significant disease. Other proposed mechanisms include altered immune responses, coelomic metaplasia, stem or progenitor cell contributions, genetic susceptibility and changes in the pelvic microenvironment.
Endometriotic lesions can establish their own inflammatory and vascular environment, allowing persistence and growth. Oestrogen signalling promotes biological activity, while inflammatory mediators and nerve growth can contribute to pain. These interacting mechanisms explain why Endometriosis cannot be reduced to a single cause and why treatments that suppress ovarian hormonal activity can reduce symptoms without necessarily eliminating every lesion.
Common manifestations include dysmenorrhoea, chronic pelvic pain, deep pain during or after sexual activity, pain with bowel movements or urination when lesions affect relevant pelvic structures, fatigue and difficulty conceiving. Some people have no symptoms and are diagnosed incidentally during evaluation for another reason. The relationship between lesion location and symptoms is imperfect because pain can involve inflammation, fibrosis, adhesions, nerve sensitisation and central pain-processing changes.
Endometriosis can also coexist with other causes of pelvic pain, so finding lesions does not automatically prove that every symptom originates from them. The condition can affect physical activity, sexual health, sleep, education, employment and psychological wellbeing. The long diagnostic pathway reported by many patients reflects the non-specific nature of symptoms and the historical tendency to underestimate severe menstrual and pelvic pain.
Endometriosis can be described according to different anatomical patterns, including superficial peritoneal disease, ovarian endometriotic cysts called endometriomas, and deep disease involving structures beneath the peritoneal surface. Deep disease may involve the bowel, bladder or other pelvic tissues and can cause organ-specific symptoms. Adhesions can distort normal pelvic anatomy and contribute to pain or impaired fertility. The visual appearance of lesions varies, and disease can be subtle or atypical rather than always appearing as classic dark lesions. Classification systems can describe extent or stage, but stage does not reliably predict pain severity or overall quality of life. This is an important clinical distinction: anatomical burden, symptom burden and reproductive impact are related but not interchangeable dimensions of the disease.
Diagnosis begins with clinical history and examination, followed where appropriate by imaging. Pelvic ultrasound is particularly useful for detecting endometriomas and certain forms of deep Endometriosis, while specialist ultrasound or magnetic resonance imaging can provide additional anatomical detail in selected cases. Imaging cannot reliably exclude superficial disease, so a normal scan does not necessarily mean that Endometriosis is absent.
Laparoscopy can directly visualise lesions and permits surgical treatment, but modern practice does not require every suspected case to undergo immediate diagnostic surgery when symptoms can be managed clinically and imaging is informative. Blood biomarkers have been investigated extensively, but no simple blood test currently provides a universally reliable diagnosis. The diagnostic strategy therefore balances symptoms, examination, imaging, treatment response and the risks and benefits of invasive investigation.
Treatment is individualised according to pain, fertility goals, lesion characteristics, previous treatments and personal circumstances. Non-steroidal anti-inflammatory medicines can reduce pain for some people, while hormonal therapies can suppress ovulation or alter hormonal stimulation of endometriotic tissue. Options include combined hormonal contraception, progestogen-based treatments and other specialist hormonal suppression strategies. Surgery can remove or destroy visible lesions and release adhesions, with the approach depending on anatomy and expertise.
Surgical treatment can improve symptoms in selected patients but does not guarantee permanent eradication because disease can recur. Fertility treatment may be considered when Endometriosis contributes to infertility, with decisions based on age, ovarian reserve, disease extent and other reproductive factors. Multidisciplinary care can be useful when bowel, bladder, pain or psychological consequences are substantial.
Endometriosis is a chronic condition whose course varies markedly. Some lesions remain stable, some progress and symptoms can change independently of visible anatomical disease. Recurrence after treatment is possible, particularly while ovarian hormonal cycling continues. The condition has substantial economic and social consequences through healthcare use, reduced productivity, missed education and work, and the long-term burden of chronic pain. Research is examining inflammatory pathways, hormonal signalling, genetics, immune mechanisms, pain processing and non-invasive diagnostic methods.
Earlier recognition is an important research and clinical goal because prolonged untreated symptoms can contribute to persistent pain mechanisms and substantial disruption of life. Nevertheless, diagnosis should remain evidence-based because many other conditions can cause pelvic pain and not every symptom occurring around menstruation indicates Endometriosis.
A common misconception is that Endometriosis is simply ordinary menstrual tissue located in the wrong place and that its severity can be judged by the size or number of lesions. In reality, the tissue resembles endometrium but has distinct biological behaviour, and symptom severity does not consistently correspond to anatomical stage. Another misconception is that pregnancy permanently cures Endometriosis; symptoms may change during pregnancy because ovarian cycling is altered, but pregnancy is not a definitive treatment.
Hysterectomy also does not necessarily eliminate all disease if lesions exist outside the uterus. Endometriosis should therefore be understood as a chronic inflammatory and oestrogen-responsive disorder involving multiple biological and pain mechanisms. Its recognition is particularly important when menstrual or pelvic pain is persistent, progressive or sufficiently severe to impair normal life.
