Dermatological sacs, also known as CYSTS, are small, closed sacs that can form in the skin. They are filled with a variety of substances such as air, fluid, or semi-solid material. CYSTS can occur anywhere on the body and can range in size from very small to several inches in diameter. They can be caused by a variety of factors including infection, inflammation, trauma, or blockage of a gland or follicle. Treatment for CYSTS may include draining, antibiotics, or surgical removal.