<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, I have irregular appearing scalp, abnormal appearing skin, arm lump or mass, lump or mass of breast, and skin swelling. What could be wrong with me?  <response>: Based on your symptoms, it is very likely that you have a sebaceous cyst. It is a common noncancerous cyst that develops in the skin, filled with a cheese-like substance. 