There is currently no reliable, noninvasive biomarker for eosinophilic esophagitis (EoE), a chronic allergic diseases characterized by significant infiltration of eosinophils in the esophagus. Because eosinophils release nitric oxide, levels of exhaled nitric oxide (FeNO) are used routinely for guiding treatment in subsets of patients with asthma. FeNO levels are also elevated in immunological diseases that do not involve the airways. The investigators hypothesize that patients with EoE have elevated nitric oxide concentration in their exhaled breath and that changes in FeNO levels could be used to measure disease activity. The objective of this study is to determine the feasibility of using FeNO as a noninvasive surrogate marker for EoE disease activity. The investigators propose to measure serial exhaled nitric oxide (FeNO) levels on a group of patients with confirmed EoE, before, during and after the course of topical corticosteroid therapy to determine whether the level declines from pre-treatment level in individual patients.