While it was thought that acne is linked to an excess of C. acnes, it is the balance of strains of C. acnes that could be the real issue. Relative to other commensals, C. acnes is normally at a low level on the skin surface, but it is by far the most predominant skin microbiota species within hair follicles.11

People with unaffected skin may actually have higher levels of follicular C. acnes than those with acne, suggesting it is not necessarily the quantity that is influencing the acne. Instead, recent research indicates certain pathogenic strains or phylotypes of C. acnes are present in acne patients. These strains may also have more potent inflammatory properties affecting acne severity when other host or environmental factors are present.

Another issue is the development of biofilm, which are complexes of bacteria and exudates that can attach to a surface. C. acnes can develop biofilms which may be more resistant to traditional antimicrobials than free-cell bacteria. People with acne may be nearly three times as likely to have C. acnes biofilms than those with healthy skin.