A microbial aetiology of acne: what is the evidence?

A microbial aetiology of acne has been suggested since the beginning of the last century. There is considerable evidence, circumstantial at best, which suggests that micro-organisms, particularly Propionibacterium acnes, are important in the pathogenesis of acne vulgaris. However, it is still unclear whether P. acnes is actually a causal agent in the development of noninflamed or inflamed acne lesions. Based on a review of the microbiological data on normal and acne-affected skin, we propose that P. acnes neither initiates comedogenesis nor has a role in the initiation of inflammation in inflamed acne lesions.