Sarcoidosis is an autoimmune disease where the immune system attacks the body's tissues, causing inflammation and formation of granulomas (clusters of cells). It most commonly affects the lungs and lymph nodes in the chest, but can impact multiple organs like the skin, eyes, liver, and heart. Symptoms vary depending on the affected organs but may include cough, shortness of breath, skin lesions, eye irritation, and joint pain. Diagnosis involves tests like chest x-rays, blood tests, and biopsies to rule out other potential diseases. Treatment typically involves corticosteroids to reduce inflammation, though some cases resolve without treatment.