Sebaceous cysts and epidermoid cysts are often talked about interchangeably, but they are different.
True sebaceous cysts arise from hair follicles, whereas epidermoid cysts develop from skin cells.
Sebaceous cysts often occur after a hair follicle becomes swollen.
The cysts originate from the sebaceous glands, the glands that secrete the oily matter (sebum) that helps to lubricate the skin and the hair.
Epidermoid cysts originate from the skin. The surface of your skin, known as the epidermis, consists of thin layers of cells. You constantly shed the cells.
However, when the cells move deeper into your skin instead of shedding, they can multiply, leading to cyst formation.
The cells that form the walls of the cysts secrete a protein, keratin, into the cyst. When the cyst drains, the secretions can be foul-smelling.
These cysts are sometimes hereditary. For instance, steatocystoma multiplex is a rare inherited disorder in which multiple sebaceous cysts form.
Cysts can remain small for years or they can keep growing larger. In other cases, a sebaceous cyst can disappear on its own.