Your body is constantly making new skin cells and shedding old ones from the epidermis, the outermost layer of skin. An epidermoid or pilar cyst can form when these cells move inward and multiply rather than shed from the surface of your skin or scalp. The skin cells form the walls of the cyst and keratin builds up inside. This thick, yellow substance may drain from the cyst if it ruptures.

This abnormal growth of cells may be due to skin irritation or injury such as an ingrown hair or acne lesion, or damage to a hair follicle or oil gland in your skin.

If a cyst is infected, it will be red and tender from inflammation. Infected cysts can also have a whitish appearance due to the presence of pus.

Cysts that do not bother you and are not infected can be left alone. You should seek treatment for a cyst if it becomes infected or ruptures. A ruptured cyst will eventually heal without treatment but will return over time.

Treatment options for a cyst will depend on its size, location, and whether it is infected. If a cyst becomes infected, the dermatologist will need to drain it by making a small incision in the cyst and squeezing out the contents. Do NOT attempt to do this yourself at home. Doing so can make the infection worse. You may also be prescribed a course of antibiotics.

If a cyst ruptures or causes problems due to its size or location, the dermatologist can remove it in the office. This minor surgery involves numbing the area with a local anesthetic injection and cutting out the cyst. If the cyst is infected, the doctor will wait until the infection has cleared up.