Odor perception in patients with multiple chemical sensitivity.

Since symptoms typical for multiple chemical sensitivity (MCS) are induced by exposure to low levels of chemicals, we hypothesize that MCS represents an impaired recognition of odors or an increased emotional reaction to common odors. Twenty-five subjects with MCS, 20 women and 5 men, and 50 gender-and-age matched controls participated in this study. The University of Pennsylvania Smell Identification Test (UPSIT) and the Cross-Cultural Smell Identification Test (CC-SIT) were administered. In addition to selecting the most probable odor among the four, the subjects were asked their impression of each odor. Odor identifiability evaluated by the scores of two tests, were almost equal in MCS and control groups. The mean CC-SIT odor per person with pleasant feeling was lower in MCS than in controls. The mean odor per person creating an unpleasant sensation was higher in MCS than in the controls. Gingerbread was the only odor making MCS subjects more pleasant than the controls. Nine out of 40 UPSIT odors were felt as unpleasant by MCS subjects more than by controls. This study indicates that MCS subjects are able to identify the odors equally as well as the controls but feel unpleasant to a larger number of odors than the controls. Despite unknown mechanisms of the altered odor perception in MCS, the application of these tests for diagnostic procedure of MCS is proposed.