A sebaceous cyst is a closed pocket of tissue that is filled with oil. They are caused by a blockage of the oil gland, and can be found most commonly on the face, back, chest and scalp. The cyst can become painful over time, as more oil is secreted the cyst will grow larger. There is also a chance where the cyst can become infected, and antibiotics may be needed. A minor procedure can be done, to excise the cyst under local anesthesia. A tiny scar will remain where the cyst once used to be.