Objective: To develop, evaluate, and apply a questionnaire-based instrument for investigation of specific symptoms in idiopathic environmental intolerance (IEI), called the Idiopathic Environmental Intolerance Symptom Inventory (IEISI).
Methods: Participants with IEI to chemicals responded to 82 candidate symptoms and to three subscales of the Quick Environmental Exposure and Sensitivity Inventory (QEESI) at a test (n = 207) and retest (n = 193) occasion.
Results: The 27 most commonly reported symptoms were selected and grouped into five symptom categories. Internal consistency, test-retest reliability, and concurrent validity were found to be satisfying. Cluster analysis identified two subgroups of IEI to chemicals.
Conclusions: The results provide support for the IEISI being a reliable, valid, and fast tool for the study of specific symptom prevalence in IEI and encourage further study of subgroups.