The objective was to provide a comprehensive and up-to-date review comprising the main findings on idiopathic

environmental intolerance (IEI). Based on these results, we expect to shed some light on the mechanisms potentially involved in this pathology as well as its nosological location. A database search was performed from 1985 to August 2014. Overall, 130 studies fulfilled the inclusion criteria. Women are at high risk for IEI. Subjects with IEI exhibit higher rates of internalizing disorders (especially somatoform disorders) as well as neurotic traits. IEI is not associated with a consistent pattern of neurocognitive deficits. IEI may be triggered by chemical exposure in some vulnerable subjects. IEI subjects display higher concerns regarding chemical environmental threats and pay more attention to related stimuli. Classical conditioning as well as sensitization processes may explain generalized reactions to several chemical stimuli. Cultural modeling may play a role in the phenomenology of IEI. IEI subjects are not more sensitive to chemical substances but are more easily disgusted and display increased activation of anterior cingulate cortex during olfactory stimulation. Some genetic polymorphisms may confer greater susceptibility for IEI. There is no consistent evidence concerning toxicological findings involved in IEI. Higher impairment among IEI subjects is mainly associated with phobic avoidance of context stimuli. Evidence-based treatments are limited and are focused on reducing dysfunctionality and distress rather than cognitive distortions. Findings support a biopsychosocial approach to IEI. Data also suggest that IEI may be conceptualized as a somatoform disorder rather than an anxiety or psychotic disorder.