Functions of the skin microbiota in health and disease.

The skin, the human body's largest organ, is home to a diverse and complex variety of innate and adaptive immune functions. Despite this potent immune system present at the cutaneous barrier, the skin encourages colonization by microorganisms. Characterization these microbial communities has enhanced our knowledge of the ecology of organisms present in normal skin; furthermore, studies have begun to bring to light the intimate relationships shared between host and resident microbes. In particular, it is apparent that just as host immunological factors and behaviors shape the composition of these communities, microbes present on the skin greatly impact the functions of human immunity. Thus, today the skin immune system should be considered a collective mixture of elements from the host and microbes acting in a mutualistic relationship. In this article we will review recent findings of the interactions of skin microbial communities with host immunity, and discuss the role that dysbiosis of these communities plays in diseases of the skin.