DefinitionA sebaceous cyst is a closed sac under the skin filled with a cheese-like or oily material.See also:CarbuncleCystFuruncleAlternative NamesEpidermal cyst; Keratin cyst; Epidermoid cyst Causes, incidence, and risk factorsSebaceous cysts most often arise from swollen hair follicles. Skin trauma can also induce a cyst to form. A sac of cells is created into which a protein called keratin is secreted.These cysts are usually found on the face, neck, and trunk. They are usually slow- growing, painless, freely movable lumps beneath the skin. Occasionally, however, a cyst will become inflamed and tender.SymptomsThe main symptom is usually a small, non-painful lump beneath the skin. However, if it becomes infected, you may have redness, tenderness, or increased temperature of the skin over