Not getting used to the smell – Chemical intolerance as lack of habituation

• Background:Chemical intolerance is a prevalent, medically unexplained symptom characterized by diverse symptoms following weak chemical exposure. The symptom-eliciting exposures are often odorous, and include perfume, fabric softeners and fragrant flowers. Several explanatory mechanisms have been proposed, but empirical data is scarce. By reanalyzing data from previous studies, we aimed to find a criterion for chemical intolerance based on reactions to actual chemical exposure.Method:We grouped participants from six previous studies based on their pattern of habituation to weak olfactory (amylacetate and n-butanol) and trigeminal (CO2 and acrolein) compounds. In two studies utilizing event-related potentials, and one functional magnetic resonance imaging study, stimuli were presented intranasally using a dynamic olfactometer. An exposure chamber that allowed full body exposure was used in the remaining three studies.Results:Individuals who did not habituate to weak chemical exposure, compared with those who did, reported (1) increasing symptoms during the course of the exposure, (2) greater problems with odors in everyday life, and (3) greater levels of everyday distress. They (4) performed worse on cognitively demanding tasks during exposure, and differed in measures of (5) the autonomic nervoussystem(respiratoryrateandpulseratevariability),(6)low-level inflammation and oxidative stress, and (7) the so called pain matrix of the brain.Discussion:Lack of habituation to weak chemical exposure may be a fruitful method of defining a sub-group of chemical intolerance.

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MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap -- Arbetsmedicin och miljömedicin (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences -- Occupational Health and Environmental Health (hsv//eng)

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