There is no single, identifiable cause of acne. Instead, there are a number of different causes of acne, each of which causes acne of a particular clinical type. The process by which acne develops is a bit like a chain reaction. At the end of the chain is the development of spots on the skin of the acne sufferer. An acne spot is the the result of body's inflammatory reaction to the presence of a comedo, a sticky mass of dead skin cells, bacteria and sebum which blocks a hair follicle. It is not known what triggers the body's inflammatory reaction to comedones, which may have lain dormant for months or even years, and causes acne spots to develop. What is known is that the development of comedones is the result of a combination of factors, which together produce conditions within the hair follicle which encourage comedones to form. The factors implicated in the development of comedones are: