A sebaceous cyst (also called epidermal cyst, keratin cyst, or epidermoid cyst) is a closed sac or cyst below the surface of the skin that fills with a fatty white, semi-solid material called sebum. Blocked sebaceous glands, swollen hair follicles, or trauma to the skin can cause such cysts. The scalp, ears, genitals, and face are common sites for sebaceous cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. They are smooth to the touch, vary in size, and are generally round in shape.

Sebaceous cysts are not cancerous and do not generally require medical treatment. However, if they continue to grow, they may become unsightly, painful, infected, or all of the above. Surgical excision of a sebaceous cyst is a simple procedure to completely remove the sac and its contents. An infected cyst may require oral antibiotics or other treatment before excision.