A cyst is a sac that is filled with a fluid or semi-fluid material. Cysts develop in various places in the body and arise from different tissues in the body. Two of the most common types of cyst that occur under the skin surface are epidermoid and pilar cysts.
This is a companion discussion topic for the original article at https://patient.info/skin-conditions/epidermoid-and-pilar-cysts-sebaceous-cysts-leaflet