In a series of investigations using 20% azelaic acid cream as a therapy for acne, it was found that the treatment, compared with its placebo, significantly reduced inflamed lesions after 1 month and non-inflamed lesions after 2 months. No changes in sebum excretion rate occurred, but a significant reduction, 15.9 to 10.5%, of free fatty acids of skin surface lipid was detected after 1 month. The follicular Micrococaceae density was significantly reduced after 1 month, and after 2 months there was a significant reduction in follicular Propionibacterium spp density. The final reductions were 2,500 and 44 fold, respectively.