An autoimmune disease occurs when the body's immune system mistakenly attacks its own healthy cells, tissues, or organs. This happens because the immune system, which is designed to protect the body from infections and diseases, misidentifies normal cells as harmful invaders. Common examples of autoimmune diseases include rheumatoid arthritis, lupus, and type 1 diabetes. The exact cause of autoimmune diseases is not fully understood, but they can be influenced by genetic, environmental, and hormonal factors. Symptoms vary widely depending on the specific disease and can include fatigue, pain, and inflammation. Early diagnosis and treatment are essential for managing these conditions effectively.