The question of chemical sensitivity is no less controversial than that of food intolerance – if anything it is more hotly debated. But whereas there is good evidence to support the idea of food intolerance there is almost no scientific data about chemical sensitivity. Belief that the phenomenon exists is simply based on seeing individual patients who get well when they avoid certain chemical exposures.
A great many doctors feel that chemical sensitivity is improbable – a dubious diagnosis that probably covers up for psychosomatic illness, hyperventilation, or purely psychological symptoms. Convincing them otherwise would take double-blind trials and a plausible explanation of how the sensitivity might arise. Double-blind trials are difficult to perform with chemical-sensitive patients for a variety of reasons. Firstly, it would be impossible to try out many of the gases and solvents ‘blind’ because they have a powerful smell – the patient would know what was being tested. Secondly, many of the symptoms produced are highly subjective – headache, confusion or nausea, for example. These are very difficult to measure objectively.
Looking for a plausible mechanism is slightly easier, but the search has only just begun, and there are few clues to go on at present. Later in the chapter, we will consider the various possibilities in this area. First we need to look more closely at ‘chemicals’ and discover exactly what they are.