Conclusion
Numerous studies have now reported that the composition of the skin microbiome is closely associated with AD flares, severity, and response to various treatment modalities. However, skin microbiota is not the sole factor in AD where genetics, immunology and environmental influences also play important roles.
Several gaps in the existing literature remain to be filled and it is hoped that future studies will address these (Table 1). Many studies currently demonstrate differences in skin microbiota composition in cases and controls at a single timepoint, which limits our ability to make conclusions about causality and temporal progression; or focus on bacterial species alone but do not explore other microbes such as viruses and fungi or their interactions with bacteria and the host. There is also a lack of mechanistic understanding of functional units in the skin microbiome and whether differences in microbial abundance impacts clinical disease or are mere bystanders reflecting fluctuations in clinical disease.
Future research should focus on several broad areas: (1) A mechanistic understanding of whether skin microbial shifts modulate or merely reflect AD and FA pathogenesis, treatment response or disease prevention; (2) Functional analysis of all skin microbes including bacteria, viruses, fungi and mites in deep metagenomic studies integrated with culture methods and skin barrier function analysis to understand their potential interactions with each other to impact disease phenotypes or progression; (3) Longitudinal studies to identify the window of opportunity for intervention, if any; (4) Evaluating the efficacy, sustainability and patient selection for microbe-based biotherapeutics in disease treatment and prevention. (Table 1).
Several interventional trials that are underway in children with AD focus mainly on monitoring skin microbiota changes in response to treatment and microbiota-based interventions, such as probiotics in topical creams and vaginal microbiota seeding (Table 2). However, apart from the latter study, the majority of these trials plan only to document changes in skin microbiota composition as secondary aims. There is a clear need for more robust studies to fill the gaps described above, and to move the field away from merely descriptive studies to understanding the mechanistic role and functions of skin microbiota in disease pathogenesis and treatment, and to evaluate the potential to harness them for targeted biotherapeutic interventions or as validated biomarkers of disease.