A sebaceous cyst is a closed sac under the skin filled with a cheese-like or oily material.
Epidermal cyst; Keratin cyst; Epidermoid cyst
Causes, incidence, and risk factors
Sebaceous 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.