Endometriosis, a painful, debilitating condition affecting 10% of women worldwide, occurs when tissue similar to the lining of the uterus grows elsewhere in the body, usually within the pelvis. The disease, which affects the immune system and causes 'ripple effects across the body', can cause symptoms such as brain fog, fatigue, joint pain, and severe brain fog. It is also known as a disease of the whole immune system, which may extend into the bloodstream and other body systems. This could explain why symptoms often occur far beyond pelvic pain and why treatment often does little to reduce symptoms. However, it could also help patients understand that their symptoms are not imagined or unrelated, but biological consequences of ongoing inflammation, not secondary effects of pain. A recent study found that people with endometria had higher levels of cytokines (IL-6) and IL-1β in their blood compared to those without the condition, suggesting an overlap between the disease and autoimmune diseases. The study also suggested that people suffering from the disease may have more severe symptoms due to their autoimmune condition than they did not have the condition.