Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids that can be easily absorbed in the small intestine[1]. Pepsin is stable at pH ranges as high as pH 6. Above this pH, pepsin is rapidly irreversibly inactivated and elevation of pH of the reaction mixture to pH 8 results in complete inactivation of pepsin[2]. Pepsin has been posited to be a reliable biological marker of EER. An immunologic pepsin assay of combined sputum and saliva was determined to be 100% sensitive and 89% specific for detection of EER (based on pH-metry), and an enzymatic test of nasal lavage fluid (100% sensitivity and 92.5% specificity) demonstrated an increased incidence of EER in patients with chronic rhinosinusitis[3]. Cultured hypopharyngeal epithelial (FaDu) cells were exposed to human pepsin (0.1 mg/mL) at pH 7.4 for either 1 hour or 12 hours at 37°C and both mitochondria and Golgi complexes were clearly damaged. This finding reveals a novel mechanism by which pepsin could cause cell damage, potentially even in nonacidic refluxate[4].