The skin microbiome: impact of modern environments on skin ecology, barrier integrity, and systemic immune programming

Abstract

Skin barrier structure and function is essential to human health. Hitherto unrecognized functions of epidermal keratinocytes show that the skin plays an important role in adapting whole-body physiology to changing environments, including the capacity to produce a wide variety of hormones, neurotransmitters and cytokine that can potentially influence whole-body states, and quite possibly, even emotions. Skin microbiota play an integral role in the maturation and homeostatic regulation of keratinocytes and host immune networks with systemic implications. As our primary interface with the external environment, the biodiversity of skin habitats is heavily influenced by the biodiversity of the ecosystems in which we reside. Thus, factors which alter the establishment and health of the skin microbiome have the potential to predispose to not only cutaneous disease, but also other inflammatory non-communicable diseases (NCDs). Indeed, disturbances of the stratum corneum have been noted in allergic diseases (eczema and food allergy), psoriasis, rosacea, acne vulgaris and with the skin aging process. The built environment, global biodiversity losses and declining nature relatedness are contributing to erosion of diversity at a micro-ecological level, including our own microbial habitats. This emphasises the importance of ecological perspectives in overcoming the factors that drive dysbiosis and the risk of inflammatory diseases across the life course.

Keywords: Allergy; Antibiotics; Biodiversity; Caesarean section; Colonisation; Cytokines; DOHaD; Ecosystems; Inflammation; Microbiome; Microbiota; NCDs; Pregnancy; Prevention; Skin.

Fig. 1

The interdependent mutualistic relationship between commensal microbes and the host maintains tissue homeostasis, inhibiting local inflammation. Regulatory responses generated in the skin also have systemic immunomodulatory effects

Fig. 2

Both exogenous and endogenous factors interact with the physical and functional aspects of the skin barrier unit – through effects on both host cells and the skin microbiome – to alter both the integrity and the activity (hormonal, metabolic, and immune) of the skin

Fig. 3

Erosion of environmental ecosystems is affecting biodiversity and microbial ecology. Together with declining nature-relatedness this is reducing human contact with immunomodulatory organisms found in natural environments – reflected in differences in skin microbes. This is increasingly being recognised as a risk factor for chronic inflammatory diseases

Fig. 4

Early life is a critical period for establishment of both the microbiome and immune responses, with long term implications for health. Understanding modulating factors during this period could lead to targets for disease prevention