Cysts are a closed sack like structure that can develop anywhere on or within the body. There are abnormal outgrowths and are usually filled with liquid, semi-solid or gaseous materials. Sometimes they can be microscopic and sometimes big enough to displace an organ. They appear as capsules and have their own distinct membranes, which are known as cyst walls. If these capsules get filled with pus, they are known as an abscess. Some cysts are harmless and are caused due to the blockage of body’s natural drainage in certain areas. However, other cysts are quite harmful, especially if they develop as tumors in the vital body organs, for e.g. keratocysts and dermoid cysts.