Microbiome network: a robust biomarker of skin health.

The skin microbiome is an integral part of the skin barrier. Its activity is shaped by microbe-microbe and microbe-host interactions. Understanding such interactions is an evolving field essential for uncovering the ecology and functions of a human microbiome community. Various studies have adapted network theory to explore the relationships of the microbiome community and its functional importance in health and diseases. The microbiome network is described as a biomarker depicting the interaction or correlation between two species, rather than their concentrations or abundances as in traditional molecular biomarkers. In skin diseases, the collapse of microbial community network structure has been reported in patients with atopic dermatitis, vitiligo and seborrhoeic dermatitis. More recently, we have reported that a fragile skin microbiome network is becoming a marker consistently observed across skin conditions, such as acne, in preclinical concerns like dry skin and premature ageing, as well as in pollution-compromised skin. In this review, we describe how advanced microbiome networks are constructed to reveal hidden microbiome features based on the nature of polymicrobial interaction from a systems perspective. We discuss the skin microbiome network as a robust network biomarker by capturing skin-microbiome interactions, specifically in conditions where a differential abundance of microbial species is absent, and further as a dynamic network biomarker by capturing skin microbiome dynamics.