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Environmental intolerance (EI) is an embracing term for a number of conditions characterized by a wide range of non-specific symptoms attributed to certain environmental exposures (e.g. pungent/odorous chemicals, residing in a certain building, electromagnetic fields and everyday sounds). EI often leads to lifestyle alterations (e.g. not taking part of activities formerly engaged in) and functional impairment (e.g. not being able to work, social deprivation). The etiology of the conditions is largely unknown, though there is growing empirical evidence for associations between mental ill-health and EI. However, mainly cross-sectional studies have been conducted which cannot demonstrate temporality. Further on, the prognosis for EI is not well-known.

This thesis includes four studies based on cross-sectional (Study 1) and longitudinal (Study 2-4) data from the Västerbotten Environmental Health Study (VEHS). The VEHS contains data from three data collections performed on the same set of respondents in 2010 (T1; n=3406), 2013 (T2; n=2336) and 2016 (T3; n=1837). In Study 1 the co-prevalence between EI attributed to chemicals, certain buildings, EMFs and sounds was investigated. The co-prevalence between all types of self-reported EI was greater than predictions based on coincidence, indicating that the different types of EI are associated, possibly sharing the same pathogenesis or that the afflicted individuals share some common predisposition to acquire the conditions. In Study 2 coping strategies and social support in EI were investigated and particularly whether certain combinations of different types of coping and social support may be important in recovering from EI. The participants who recovered from EI showed different combinations of coping strategies and social support than those who did not recover. In Study 3 the temporality between EI (attributed to chemicals, buildings and sounds) and psychological factors was investigated. The results showed that stress, anxiety, depression and burnout are risk factors for EI attributed to chemicals and sounds, but not for EI attributed to buildings. Changing perspective, EI attributed to buildings was a significant predictor of burnout, whereas EI attributed to sounds and chemicals were not. In Study 4 the prognosis of EI during a six-year period was studied. The probability of recovering from a state of specific EI was 44.3%, the probability of a specific EI to spread to other types of EI was 12.8%, and the probability of relapse was 3.9%. The participants who recovered showed lower levels of emotional and behavioral disruption than those who did not recover. The participants who showed spreading from one to several EIs perceived more stress than those who remained in a state of a specific EI, but had lower levels of burnout.

Based on the findings of the studies in the thesis it is suggested that psychotherapy focusing on reducing the emotional and behavioral reactions of exposure might be helpful. Even though the causation of EI is unknown, negative expectations about exposure might accumulate symptoms, setting a vicious circle into motion. The task of the psychologist might be to break this circle.