A skin cyst usually appears as a round bump under your skin. It may have a dark spot in the center, and it may be warm and tender to the touch. Often, a cyst easily rolls and moves under the skin, and there is some discoloration, usually slightly darker than your normal skin tone. Cysts may be as small as a quarter of an inch in diameter, or they may be as large two inches or more. Some cysts may grow in size over time.