A cutaneous cyst is a lesion that forms a cavity under the skin with semi-fluid material. Cysts are harmless, sac-like growths in the deeper layers of the skin. They form from the lining of a hair follicle that gets blocked. There are many kinds of cysts. They can appear anywhere in the body.
It is not known why cysts appear, nor why some people have a tendency to get them.
Cysts can become inflamed, infected, and the contents of the cyst can rupture into the surrounding skin. They can be red and painful and, if infected, cause significant discomfort.