A quiet scientific revolution has been taking place over the last few years as a consequence of strides in genomic science and molecular techniques. These advances have transformed the way humans view themselves as biological organisms. This revolution is the discovery of the human microbiome and with it, the realization that the human body is not simply composed of innate cells and the matrices they produce; i.e., collagen, bone minerals, etc. The body is also composed of a plethora of microbes, in numbers many times that of one’s “own” cells. This idea has been addressed by the popular press, and appears to be reaching the general public now.
Most of what is known about what is collectively called the human microbiome—that is, the ensemble of all microbes and their genetic elements, living interdependently with human cells in the host—was learned by studying the gut. However, other epithelial tissues such as the oral cavity, vagina and skin are known to be areas harboring large numbers of microbes. What is particularly interesting about the skin is that its diverse properties across different sites provide different microenvironments for several types of microbial ecosystems.
For example, the composition of the microbial population in a dry skin area, such as on the leg or arm, is different than that of a moist skin area (such as the axillae), or that of an oily and sebaceous area, such as the face or the chest.1 Moreover, over time, there is a larger interpersonal variability in the composition of skin microbial populations than there is intrapersonally.2, 3 This is one more piece of evidence indicating the microbiome is not only a “passenger” on the host organism but an active contributor to an organism’s phenotype. The idea that humans are “superorganisms” composed of taxonomically diverse ecosystems argues against the simplistic view of “good” and “bad” microbes. Thus, researchers are now looking more at the microbiome as a whole rather than separating out individual species.
Many organisms previously thought to be pathogens, such as Staphylococcus aureus, have been identified as members of microbial populations isolated from healthy skin.4 On the other hand, some species believed to be “commensals” are known to become opportunistic pathogens given the right environmental stimuli; for example, Staphylococcus epidermidis can form biofilms on catheters during infant intubations.5
New research hints that a diseased state may be achieved by the absence of commensal bacteria and not simply the presence of a pathogen. Researchers are therefore examining microbial diversity to assess health and disease.6 The emergence of the new field of skin microbiome research is beginning to define a way to describe skin health and disease. How this applies to the study of infant skin and what it means for the development of suitable infant skin care products is the subject of the following discussion.