A Cyst is defined as a sac containing liquid or semisolid material.
Epidermal inclusion cysts, also called ” Sebaceous cysts,” are the most common type of skin cyst and are typically located on the face and trunk. Epidermal inclusion cysts are felt to develop as a result of injury, in which the opening of the hair follicle tucks inwards, trapping skin cells inside. Cystic acne may predispose patients to the development of epidermal inclusion cysts. The cyst forms as a painless swelling in the upper layer of the skin, often with a dilated opening (see photos). Non inflamed cysts are painless, but with pressure, cyst contents can be pushed out through the opening, often with a foul odor. Squeezing a cyst can sometimes cause rupture of the wall producing an intensely painful red swelling necessitating drainage by a physician. Often a ruptured cyst looks infected (much like a boil) though most the time, this represents a foreign body reaction. It is virtually impossible to remove the sac when the cyst is inflamed.
Most cysts do not require removal unless desired by the patient. Treatment involves surgical excision, which is curative as long as the entire sac (cyst wall) is removed. Dr. Craig Singer routinely excises epidermal inclusion cysts through the use of local anesthesia.
Photos courtesy of DermnetNZ
Pilar cysts are commonly seen on the scalp. These are benign cysts derived from the root sheath of the hair follicle, and may be solitary or multiple. Pilar cysts are painless swellings and have no dilated opening. The cause for these cysts is unclear however many people have a family history of pilar cysts. Treatment involve surgical excision and removal of the sac which is typically easier than with epidermal inclusion cysts. Dr. Craig Singer routinely excises pilar cysts through the use of local anesthesia.
Bolognia, Jorizzo and Rapini. Dermatology. Second edition, chapter 110: Cysts
Dermnet NZ, www.Dermnetnz.com