Epidermoid (or epidermal) cysts are the most common skin cysts.  These can occur anywhere on the skin but are most common on the face and upper trunk.  They are usually smooth, round, skin-coloured bumps that range from a few millimetres to several centimetres in size.  They often have a black "punctum" where one sees where the pore has been blocked.

Epidermal cysts develop when a hair follicle or pore becomes blocked.  People who have acne may develop multiple epidermoid cysts in areas where their pores have been blocked.

Epidermal cysts are benign.  They do not become cancerous.  They can occasionally rupture in to the skin, causing a great deal of inflammation.  Do not pick or prod at your cyst as this makes it more likely to rupture.  

If cysts become inflamed they should be drained in order to speed healing.  Draining cysts does not remove them as they eventually refill.  See your doctor if you have an epidermal cyst that has become painful, red and swollen or has begun to discharge pus.

If cysts are bothersome they can be removed by surgical excision.    Your doctor can describe this to you in detail.