It is also not clear whether the vital balance of various species of bacteria that are found within a follicle play an important part in the initiation of acne. However, the surface of the skin in acne-prone regions is colonized by the bacteria Staphylococcus epidermidis and Propionibacterium acnes. While epidermidis microbe does not usually cause any diseases and is a normal resident flora of the human skin, it may at any time become an opportunistic infection-causing bacteria due to other factors, such as a weak immune system. A number of selective research studies show that the main bacterium associated with the development of acne is Propionibacterium acnes