A vast number of microorganisms inhabit the human body, outnumbering cells by 10-to-1, with skin being one of the largest habitats.1–4 However, science is just beginning to explain the complex relationships between microbes and the human body, in addition to cosmetic and drug products applied to skin. Until recently, methods used to identify and study the skin’s microbiota relied on the ability to culture individual species in the laboratory. Now, sequence-based metagenomic techniques allow for the analysis of entire environmental niches and have demonstrated that previous culture techniques substantially under- estimated the skin’s microbial population and diversity.5 Using these technological advances, the Human Microbiome Project has already begun to dramatically change the understanding of skin’s microbial ecology.6 Goals of the present project aim to identify the role of this microbiome not only in disease, but also in the maintenance of health.3, 7
As science continues to elucidate the nature of interactions with microbiota, the question arises as to whether it may be possible to selectively harness the benefits of some organisms while protecting against the potential dangers of others.3, 8–10 Specifically, understanding the relationship between the skin and its microbial inhabitants presents an interesting approach to cosmetic formulation for maintaining or improving skin health.
Normal Human Skin Microflora
The establishment of one’s normal skin flora typically occurs during delivery as a newborn.11 It consists of several major groups of bacteria, comprised of staphylococci, coryneform bacteria, micrococci and Gram-negative bacilli, in addition to the Malassezia genus of yeasts.12 Populations vary by body site and factors such as skin hydration and availability of nutrients.13 Clinical data on the number and types of organisms inhabiting the skin from culture-based techniques is abundant, but there is little understanding of the mutualistic and commensal relationships of these organisms with their habitat.10