Environmental intolerance (EI) is a condition characterized by low tolerance to environmental stimuli at levels that would not affect most people. EI is an ill-defined condition from which sufferers experience highly individual multisystem symptoms following exposure from specific environmental sources. Most research on EI is conducted using cross sectional approaches, however, longitudinal approaches that capture daily exposure are needed to fully understand how EI develops and change over time. This paper describes an app that was developed that can be used with most smartphones and, in conjunction with a website, can be used to collect symptoms and ratings of discomfort in the field as well as qualitative reports of the incident that triggered the discomfort.