A variety of different types of cysts occur on the skin. The most common is a sebaceous or epithelial cyst which can arise in oily portions of the skin. A cyst is characterized by a small sac which contains oily material and which is a result of blockage of the oil gland. Sometimes there is a hereditary tendency to develop these. A cyst can be removed by surgical excision. If left untreated, some cysts may rupture and create a large abscess which requires more aggressive therapy.