Sebaceous cysts are small lumps that arise within the skin on the face, upper back and upper chest. A sebaceous cyst can form when the opening to a sebaceous gland becomes blocked. The oily substance called sebum continues to be produced but cannot escape to the outer skin surface.
The cyst may remain small for years, or it may continue to get larger. These cysts are rare in children but common in adults. Sebaceous cysts are not cancerous.