Recent studies have revealed the existence of diverse and complex microbial populations in the skin, digestive, respiratory, and reproductive tracts of humans and animals. These populations vary across individuals, and the term microbiome may refer to the organisms themselves or their collective genes. It is surmised that there are 10 times more microbial cells on the human body than human cells. The important functional genes of the microbiome can influence host health and are important in understanding maintenance of host health.
The skin microbiome varies across both body sites and individuals and is influenced by age, sex, diet, hygiene, lifestyle, and amount of time spent indoors vs outdoors. Cohabitation among individuals from different species (eg, humans, dogs) contributes to a more diverse skin microbial population, which is now considered to be a key component in immune regulation. Imbalances in the skin microbial population may be associated with inflammatory skin conditions such as atopic dermatitis.—Hoffman AR