A cyst is a sac containing fluid, gas, or air that can occur anywhere in the body or under the skin. It is generally non-cancerous and does not cause pain. The sizes can differ from being microscopic to massive structures resulting in internal organ displacement.

Some of the causes of cysts include:
infections
blockages in ducts resulting in fluid build-up
genetic conditions
parasites
chronic inflammation
a cellular defect
faults during embryonic development
an injury breaking a blood vessel

A cyst is a capsular structure produced by an outer layer of abnormal cells, while an abscess contains pus due to infection by bacteria, virus, or fungus. A cyst develops slowly and is painless. However, an abscess is painful, reddish in colour, swollen, irritated, and it can spread the infection to other parts of the body. A cyst can transform into an abscess if it gets infected.

Some of the types of cysts include:
epidermoid cyst - produced due to trauma around a hair follicle in the skin
ganglion cyst - forms in joints, for example on the wrist
ovarian cyst - results in build-up of fluids on or within ovarian surface
breast cyst - caused by fluid accumulation near the glands in the breasts
chalazia - forms when there is a blockage in the oil ducts of the eyelids

A biopsy is done to establish if the formed cyst is benign or malignant. Usually, the cysts go away on their own. If they do not, then it is drained with the help of a needle or removed surgically by a doctor. Antibiotics or corticosteroid injections might be needed to reduce the inflammation caused by the cyst.