Fig. 5. Potential modifiers of lower airway microbiome course.

The dynamic nature of the lower airway microbiome is ever evolving. The overarching factors that control the balance of the microbiota are microbial immigration via inhalation and microaspiration and microbial elimination via cough, mucociliary transport and immune responses. We postulate that factors such as vaginal delivery⁸⁷, exercise and a healthy diet may contribute towards eubiosis in the lower airway, whereas obesity, an unhealthy diet and frequent antibiotic use could disrupt the lower airway microbiome in an unfavourable manner. Finally, we surmise that lower airway immune resilience and the diversity of the lung microbiome (a symbol of health in its own right) follows a quasi-sinusoidal path, peaking in adulthood.