Chitosan demonstrates antimicrobial effect against P. acnes and S. aureus . Chitosan was incubated with bacteria for 3 hours to assess antibacterial activity. Bacteria was then enumerated by colony-forming unit assay to determine concentration, which was plotted as a percentage of untreated sample. Error bars represent SEM (n = 4, independent experiments). *p < 0.05 and **p < 0.01 (t-test).