Cysts are closed sacs filled with fluid, air, or other substances that can form in various parts of the body. They can vary in size and may develop in organs, tissues, or under the skin. Most cysts are benign, meaning they are not cancerous, and often do not cause any symptoms. While many cysts require no treatment, some may need to be drained or removed if they become painful or infected. Common types of cysts include sebaceous cysts, ovarian cysts, and baker's cysts. Regular check-ups can help monitor any changes in cysts over time.