We are used to explanations of the complexity of the human gut, with trillions of microbes representing thousands of species, comprising a gut microbiota invaluable to our health and the proper development of our immune systems. But there are two other complex surfaces in the human body that are also incredibly important to the commensal microbes that live on and in us. One is the lining of the lungs and the bronchial passages and the other is the skin. Skin is much more three-dimensional than we sometimes realize and is a very complex ecological area with numerous anatomical niches or a wide variety of microorganisms that are impacted by the detergents we clean our bodies with, skin conditions, and physical scarification. This paper explains the technology now available to describe the ecological complexity of skin in sufficient detail to really extend the hygiene hypothesis to this huge organ. Here is the abstract and the full paper is open access through the link above.
The human skin is an organ with a surface area of 1.5–2 m2 that provides our interface with the environment. The molecular composition of this organ is derived from host cells, microbiota, and external molecules. The chemical makeup of the skin surface is largely undefined. Here we advance the technologies needed to explore the topographical distribution of skin molecules, using 3D mapping of mass spectrometry data and microbial 16S rRNA amplicon sequences. Our 3D maps reveal that the molecular composition of skin has diverse distributions and that the composition is defined not only by skin cells and microbes but also by our daily routines, including the application of hygiene products. The technological development of these maps lays a foundation for studying the spatial relationships of human skin with hygiene, the microbiota, and environment, with potential for developing predictive models of skin phenotypes tailored to individual health.