Cosmetic and personal care products must be adequately preserved to withstand microbial insult from routine consumer use. Humans are host to an extensive assortment of microorganisms, and while normal flora play an essential role in skin health, some may become pathogenic under certain conditions; e.g., if microorganisms gain access to deeper tissues as a result of trauma, surface breaks and wounds. Normal flora may also become pathogenic if transferred to immunocompromised persons.
Cosmetics are not expected to be sterile; however, they must be produced under Good Manufacturing Practices (GMP) and be free from microorganism concentrations and types that may cause product spoilage or that may adversely impact consumer health. Furthermore, the composition of normal human skin flora is dynamic and can vary with age, environment, geographic region, exposure to antimicrobial agents and immunological state.1–5 With these considerations, the present article reviews not only the transient and resident microbes of the human skin, but also considers how cosmetic products may affect and be impacted by normal skin flora.