Sweet interference: oral fermentation volatile confounders in exhaled breath revealed by minimal glucose exposure

Volatile organic compounds (VOCs) in human breath have been explored as non-invasive biomarkers for disease, including respiratory infections and cancer, yet very few breath tests have reached clinical validation and regulatory approval. A major barrier is the difficulty of identifying and controlling confounding factors that affect volatile exhaled breath composition. A critical and overlooked confounder is the oral microbiome, which produces VOCs that can obscure the trace volatiles originating from the lower airways. To investigate this, we conducted an intervention study on sixteen healthy volunteers, using real-time breath analysis, which demonstrates that oral microbiota rapidly alter exhaled VOC profiles following a low-dose (0.5 g) oral glucose administration. Acetoin levels respond promptly to glucose, confirming its oral microbial origin. However, pathogenic bacteria resulting from respiratory infections can also produce acetoin, underscoring the challenge of distinguishing sources of breath VOCs. Similarly, other volatiles, such as acetic acid and ethanol, are also influenced by small glucose doses, complicating their use as biomarkers in non-targeted volatilomic studies. Recognising the metabolic context of each volatile is essential to distinguish infection signals from physiological background. Beyond serving as a cautionary note for exhaled breath research, these results may encourage the oral health and dentistry communities to adopt breathomics analytical tools for rapid chairside diagnostics, transforming respiratory confounders into clinical opportunities for dental care.