Sebaceous cysts — slow-growing bumps under the skin that can appear on the ears, scalp, face, torso, back, or groin area — are typically harmless. And while they can be irritating (or unsightly), they are not cancerous. The term “sebaceous cyst” is often used to describe what is actually an epidermoid cyst. True sebaceous cysts are caused by the glands that secrete the oily matter (sebum) that helps lubricate your skin and the hair. These dome-shaped cysts can be pea-sized, or grow to a few inches or larger. They grow very slowly, and they’re not painful. If you touch them, you should be able to move them around. They often have a central small black dot, or punctum, through which sebum accumulates. Sometimes, however, they can become inflamed, infected, or suddenly rupture, which can increase the risk of infection (more on that later).