Endometriosis is a painful, debilitating condition affecting 10% of women worldwide. It occurs when tissue similar to the lining of the uterus (known as lesions) grows elsewhere in the body – usually within the pelvis.
Treating endometriosis can be difficult. Usually, treatment involves either preventing the growth of these lesions in the first place or removing lesions surgically. But even when lesions have been surgically removed, symptoms often don’t go away.
Traditionally, endometriosis has been thought of as a gynaecological condition. But mounting evidence suggests this characterisation downplays the disease’s complexity. Endometriosis appears to affect far more than just the reproductive system. According to a growing body of research, it influences immune function throughout the whole body.
Recognising it as a whole-body, immune-driven disease could help explain why symptoms range far beyond pelvic pain. It would also explain why treatment is so challenging and often does little to reduce symptoms.
A disease of the whole immune system
Inflammation – the body’s natural response to injury or illness – is a normal part of immune response. It also plays a key role in the menstrual cycle.
But if inflammation becomes chronic or uncontrolled, it can cause problems. This is seen in autoimmune conditions such as rheumatoid arthritis, where the immune system overreacts even when there is no threat.
Chronic inflammation is also known to play a central role in endometriosis. But the effects of this uncontrolled immune response may be far more widespread than previously thought. According to recent research, the immune response appears to extend into the bloodstream and other body systems. This may explain why endometriosis causes such far-reaching, whole-body symptoms.
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Endometriosis: how the condition may be linked to the immune system
In people with endometriosis, immune cells appear to be less able to clear lesions. Yet, at the same time, people with endometriosis have higher levels of immune proteins such as IL-6 and IL-1β in their blood. These immune proteins, known as cytokines, are a type of messenger released by cells to promote inflammation.
Together, these dysfunctional cells make it possible for lesions to grow and persist. This immune dysregulation also has ripple effects across the body, contributing to the wide range of symptoms sufferers experience.
For instance, many people with endometriosis experience debilitating fatigue, cognitive difficulties (such as “brain fog”) and widespread pain. These symptoms are rarely emphasised in clinical guidelines, yet they’re often as disruptive as pelvic pain itself.
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Systemic inflammation offers a compelling explanation for these symptoms. Circulating cytokines, such as those mentioned earlier, are known to influence brain function and energy regulation. Higher levels of cytokines (including IL-6) have also been linked to poorer concentration, disrupted sleep and fatigue in some autoimmune and chronic pain disorders.
These same processes may be occurring in endometriosis. This suggests that invisible symptoms could be biological consequences of ongoing inflammation – not secondary effects of pain.
A dysfunctional immune system may also help to explain why emerging research hints at an overlap between endometriosis and autoimmune diseases.
In 2025, a large scale study looked at 330,000 patients with endometriosis and 1.2 million controls (people who didn’t have the condition). The study found that compared to the controls, people with endometriosis had roughly twice the odds of being diagnosed with an autoimmune condition – such as rheumatoid arthritis, lupus, multiple sclerosis or Hashimoto’s disease – within two years of their endometriosis diagnosis.
This doesn’t mean endometriosis is itself an autoimmune disease. But it does suggest shared mechanisms – including chronic inflammation, dysregulated immune cell activity, and problems with the immune system recognising the body’s own tissue properly.
These overlapping features strengthen the case for understanding endometriosis as a systemic immune disorder.
Reframing endometriosis
Viewing endometriosis in this way could transform how it’s diagnosed, treated and understood. It could also help us get closer to finding a solution for the condition.
Current treatments primarily target the reproductive system. But if endometriosis involves widespread immune dysfunction, then therapies that modulate immune pathways may offer more effective long-term relief.
Seeing endometriosis as a systemic condition can empower patients, as well. This reframing may help them understand that symptoms such as fatigue, joint pain, cognitive difficulties and immune sensitivity are not imagined or unrelated. Rather, they’re part of the condition’s broader biology.
Seeing it this way may support patients in advocating for themselves in healthcare settings, where systemic symptoms are often dismissed or deprioritised.
A systemic framing also opens space for patients to explore complementary management strategies aimed at reducing inflammation or improving overall wellbeing. While not curative, some people find gentle movement, stress regulation techniques and heat–cold contrast therapy helpful for managing pain or inflammatory flares.
A growing body of research shows that endometriosis is not solely a reproductive condition or a “bad period”. It’s a multi-system, inflammatory disorder with far-reaching health effects throughout the body.
Understanding endometriosis as a systemic immune disease is a crucial step toward better treatments, better support and, ultimately, better health outcomes.
April Rees receives funding from The Royal Society, Saint David's Medical Foundation, and the Iraqi Government.
Laura Cowley receives funding from Health and Care Research Wales, Welsh Crucible, and the Learned Society of Wales.
