What it is
C. acnes (formerly Propionibacterium acnes) lives normally within sebaceous follicles. It is part of the skin microbiome.
Specific phylotypes and biofilm states are associated with inflammatory acne, not the simple presence of the bacterium.
This is why 'killing all bacteria' is not the goal; rebalancing follicular ecology is closer to the actual mechanism story.
Why it matters
Reframes acne as ecology rather than infection: which strains, which environment, which signaling.