The researchers looked at the bacteria's gene expression and find link between vitamin B12 and acne. In the presence of vitamin B12, the skin bacteria that are commonly linked to acne start pumping out inflammatory molecules known to promote pimples.Propionibacterium acnes, the most common skin microbe, causes pimples in some people but not in others. In humans, vitamin B12 plays a key role in metabolism, red blood cell formation and the maintenance of the central nervous system and is found in multivitamins. The study was published in the journal Science Translational Medicine.