MODEL RELEASED: Out-patient surgery: preparation for excision of a sebaceous cyst on the scalp. A sebaceous cyst is formed as a result of blockage of a sebaceous (oil-forming) gland in the skin. Such cysts, which contain a smooth, yellow cheesy material are harmless but may grow very large or become infected and painful. They are removed through a small incision in the skin and provided the entire cyst wall is removed recurrence is rare.