A variety of chemicals are known to cause allergic sensitisation of the respiratory tract associated with allergic rhinitis and asthma. It is generally accepted that the development of sensitisation of the respiratory tract to chemicals is a threshold phenomenon. That is, a certain minimum level of exposure is required to induce sensitisation to a given allergen. This Task Force was set up to assess whether the corollary is true: that there will be levels of exposure below which sensitisation will fail to develop.
In common with all forms of allergic disease, chemical respiratory allergy develops in two phases. In the first phase, exposure to the inducing chemical allergen, via a relevant route, will cause immunological priming resulting in sensitisation of the respiratory tract. In the second phase, the now sensitised subject responds more vigorously if the same allergen is encountered again: the subject has become ‘sensitised’. Following inhalation exposure of the sensitised subject to the same chemical allergen, an inflammatory response will be provoked in the airways that in turn drives allergic disease.
The analyses by the Task Force have revealed that the acquisition of sensitisation of the respiratory tract to chemicals is dose-dependent and that thresholds do exist. However it is commonly difficult to define exactly what levels of exposure will be required for sensitisation to develop. It is clear that in some circumstances it may be possible to use occupational exposure data to derive levels of workplace exposure that are safe. However, the Task Force highlights the fact that there remains a need to develop improved methods for hazard characterisation.