A cyst is a capsule-like structure made of membranous tissue and can consist of fluid, gas, or air. It can form anywhere in the body or under the skin. It is generally painless and not cancerous in nature. The sizes can vary from as small as microscopic to being so large that it can lead to internal organ displacement.

Some of the causes of cysts are as follows:
infections
chronic inflammation
parasite
cellular defects
blocked ducts in the body
inherited diseases
errors during fetal development
an injury causing broken blood vessels

A cyst is a saclike structure made up of an outer layer of abnormal cells, while an abscess contains pus due to infection. A cyst usually develops more slowly and does not cause pain. However, an abscess is painful, swollen, reddish coloured, irritated, and this infection can spread and produce symptoms in other parts of the body. A cyst can sometimes change into an abscess if it gets infected.

Some of the commonly observed cysts are:
epidermoid cyst - forms around a hair follicle in the skin after trauma
ganglion cyst - forms within joints such as the wrist
ovarian cyst - occurs due to accumulation of fluid on or within the ovary
breast cyst - happens due to fluid build-up near the glands in breasts
chalazia - forms due to blockage in oil ducts of the eyelids

A biopsy is done to establish if the cyst is benign or malignant. Most of the cysts can heal on their own, or persist without any symptoms. If not, then they are either drained by making use of a needle or removed as a whole surgically. The inflammation of the cyst is sometimes treated by the use of a corticosteroid injection or antibiotics.