REVIEW Skin sensitization: risk assessment

The assessment of risk is the deciding point in the toxicology of skin sensitization. Methods for the identification of skin sensitization hazards have been available for decades. Indeed, the majority of the clinically important chemical contact allergens are known. What is required to ensure that the incidence of allergic contact dermatitis is kept to a minimum is that these known hazards are properly assessed in the context of possible skin contact. A primary step in the risk assessment process is determination of the relative skin sensitizing potency of the substance in question in relation to that of other known, clinically relevant, contact allergens. Traditional test methodologies are not well suited to this task, not least because they lack any element of dose-response assessment. A newer approach, the local lymph node assay, offers an opportunity to obtain an objective and quantitative assessment of skin sensitizing potency. Armed with this information, the risk assessor must then evaluate the nature and extent of skin exposure to the substance, remembering the spectrum of habits and practices that may occur, as well as reasonably forseeable misuse. The approach then taken to skin sensitization risk assessment is usually that of comparative toxicology, in which the new chemical is compared and contrasted with known safe and unsafe materials. Reassurance of safety may be enhanced by carefully controlled human volunteer studies, including those which are negative, but where there has been a substantial exaggeration of exposure compared to what is actually expected.