The Oral and Nasal Gateway Microbiomes: Salivaomics and Systemic Health at the Airway–Digestive Interface

Abstract

Simple Summary The oral and nasal microbiomes can be understood as a gateway ecosystem because the oral cavity connects the upper digestive tract and the upper airway. Diet, saliva, oxygen tension, breathing route, host immunity, and microbial ecology meet at this interface. This narrative review examines bacteria, fungi, viruses, and bacteriophages as members of a co-evolved oral–nasal ecosystem that supports health when balanced and contributes to disease when disrupted. Evidence associates oral and nasal dysbiosis with caries, periodontal disease, cardiometabolic disease, adverse pregnancy outcomes, respiratory disease, allergies, and cancer-associated microbial ecology. Salivaomics offers a practical, noninvasive route for earlier biological risk detection in dentistry and respiratory medicine.