Chemical hypersensitivity is a well-known entity - once sensitised to a particular substance it often results in what we call cross sensitivity, which means that such individuals become sensitised to a large group of chemicals.

Such hypersensitivity tends to be life-long and intrusive, serious symptoms may result from even relatively small doses of chemicals in the environment.

Notorious agents include organophosphates used by pest exterminators as herbicides for insect control, where chemicals are sprayed by plane the substance is often carried hundreds of kilometres and enters the food chain or is washed down the roofs into rainwater.

There are numerous celebrated cases of mass exposure to chemicals, for instance in the notorious 'Love Canal' trial which was the basis for the film 'Erin Brockovich'.
In many cases chemicals become more and more concentrated as they go through the food chain, in animal husbandry the use of antibiotics in poultry farming and grazing animals and the use of hormones ultimately affect humans.

Very often patients meet with scepticism because susceptibility is very individual, others in the same household, neighbourhood or occupation may be totally unaffected and the symptoms are often vague and seem excessive to the uninformed.

As an expert medical witness in Margaret's claim I can vouch for the accuracy of her observations and I am particularly impressed by her eloquence and lack of exaggeration.

Dr Peter Kendall MBBS BSc MRCP(London) FRCP(Edinburgh)