Correlation but not causation:

Chemical Sensitivity Tied to Anxiety, Depression

Anxiety and depression may be important features of multiple chemical sensitivity (MCS), a controversial diagnosis given to some people with apparent allergic reactions to a range of everyday exposures.

A small study of MCS patients found that they were more likely to suffer depression than either healthy individuals or people with asthma. And both asthmatics and those with MCS showed greater-than-average “anxiety sensitivity,” an exaggerated response to anxious feelings that is characteristic of panic disorder.

People diagnosed with MCS typically report a range of symptoms, from headaches and joint and muscle pain to fatigue, memory loss and depression. The medical community is divided over whether MCS actually exists, but some believe that low-level exposures to everyday chemicals like those in cosmetics, soaps and detergent trigger physical reactions in MCS patients.

Some researchers have also proposed that the psychological disorders that often accompany MCS are a reaction to the syndrome, and not the underlying cause, according to the authors of the new study. Reuters Health

While some organic basis to some MCS may exist, most of the cases I have seen seem to be of people using a physical metaphor for emotional distress. Investigation of physiological parameters, immune function, etc., in MCS show no consistent findings. This may be because it is non-physiological or because the study group is heterogeneous. A study finding consistent psychological alterations in MCS sufferers is more supportive of psychological causation of the syndrome, although the authors are hesitant to draw that conclusion [being more cautious than I am about being seen as opinionated… — FmH].