A cyst is a harmless sac-like growth in the deeper layers of the skin, which is filled with a soft, whitish brown material that sometimes oozes onto the skin surface.
Cysts are also more likely to become infected in smokers.
We do not know why cysts appear, nor do we know why some persons get many of them. Often we are born with cysts under the skin. Sometimes, people who have multiple cysts have a family history of this problem. As a person gets older, sometimes a cyst which was present since birth suddenly gets larger. When this happens, bacteria often get into the cyst and an infection occurs which can resemble a boil.