A cyst feels like a lump or bump under the skin. The majority of cysts are sacs under the skin that fill up with skin cells and other skin products. This material is a white, cheesy substance which may have an odour.
A cyst can develop for a number of reasons. Sometimes, it is because a hair follicle gets blocked. More often, a cyst occurs because cells from the surface of the skin accidentally find themselves in the deeper layers of the skin.