Is multiple chemical sensitivity a learned response? A critical evaluation of provocation studies

Background. A systematic review of provocation studies concluded that while persons with multiple chemical sensitivities (MCS) react to chemical challenges, these responses occur more often when they can discern differences between active and sham substances. The authors of the review interpreted these findings as evidence that the symptoms may not be specific to the chemical but related to expectations and prior beliefs. Given the complexity of the subject matter, the studies were re‐examined using additional criteria.Results: Our analysis revealed a number of methodological weaknesses which do not appear to have been given due consideration by the authors when interpreting the findings.Conclusions. In light of these shortcomings, we believe that their conclusions may have over‐stated the role of psychological factors in the aetiology of MCS.