 Propionibacterium acnes (P. acnes) is the anaerobic bacterium species that is widely suspected to contribute to the development of acne, but its exact role in this process is not entirely clear. There are specific sub-strains of P. acnes associated with normal skin and others with moderate or severe inflammatory acne. It is unclear whether these undesirable strains evolve on-site or are acquired, or possibly both depending on the person. These strains have the capability of either changing, perpetuating, or adapting to the abnormal cycle of inflammation, oil production, and inadequate sloughing of dead skin cells from acne pores. One particularly virulent strain has been circulating in Europe for at least 87 years. Infection with the parasitic mite Demodex is associated with the development of acne. However, it is unclear whether eradication of these mites improves acne.
