A cyst is a fluid-filled, round lump located under the skin. They are usually white or yellow in colour and may also have a dark plug in the centre. They range in size, growing slowly up to a couple of centimetres long. Cysts are normally harmless and painless unless they become infected, and are not hereditary or contagious. They can grow anywhere on the body but most commonly found on the face, neck, shoulder, chest and genitals.
Cysts are more common in women than men, occurring post-puberty and often in people who have suffered acne or have injured the skin e.g. a damaged hair follicle.