Exhaled breath condensate (EBC) is breath that has been condensed, typically via cooling into a collection device (commonly a simple glass tube or a jaeger ecoscreen)^[1]. EBC reflects changes in the respiratory fluid that lines the airways. EBC is a cheap, non invasive tool that has potential for screening or diagnosing diseases of the lung and other conditions.

Exahled breath condensate reflects the composition of the airway lining fluid. The primary constituents of EBC include:

1. Aerosolised particles of airway lining fluid collected from the airways via airflow
2. Water vapor condensation produced around the aerosolised particles
3. Water soluble volatile gases dissolved into the water vapor condensate

As EBC reflects the composition of the airway lining fluid, it contains every molecule that the fluid contains, simply in much smaller concentrations. This means it contains adenosine, nitrates, nitrites and so on. Furthemore in disease states EBC contains molecules reflective of that disease state or greater concentrations of those molecules. In patients with Gastroesophageal reflux disease patients have been demonstrated to have pepsin (usually localised to the stomach) in their EBC. Patients with COPD and asthma have been demonstrated to have increased levels of reactive oxygen species.