Risk Assessment for Contact Allergens
Contact allergens are chemical skin sensitisers which have the capacity to induce in humans a state of immunological hypersensitivity, such that subsequent exposures carry the risk of the elicitation of the skin disease allergic contact dermatitis (ACD).
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Risk Assessment for Contact Allergens David A. Basketter
7.1
Introduction
Our world is formed entirely from chemicals, the great majority of them delivering vital properties—nutrition, homes, transport, medicines, hygiene and so on. However, some of these chemicals, as well as others in the environment, also have other capacities, including the ability to combine with our proteins and thereby cause allergy. The underlying mechanisms associated with this are reviewed elsewhere in this book and will not be repeated here (see Chap. 10). This section will focus wholly on the assessment of the risk presented to human health. Before that is started though, some definitions are necessary: A skin sensitiser is a protein reactive chemical which can induce a state of delayed-type, cell- mediated hypersensitivity, which in humans is termed contact allergy. Contact allergy can be detected by a diagnostic patch test with the offending chemical. If there is a positive reaction, the individual is sensitised. The skin disease allergic contact dermatitis will be elicited in a sensitised individual where there is sufficient dermal exposure. Hazard identification and characterisation involves determining whether a particular chemiD.A. Basketter DABMEB Consultancy Ltd., Sharnbrook MK44 1PR, UK e-mail: [email protected] © Springer International Publishing Switzerland 2018 J. Krutmann, H.F. Merk (eds.), Environment and Skin, https://doi.org/10.1007/978-3-319-43102-4_7
cal possesses skin-sensitising properties and, if it does, measuring the strength of that property, commonly referred to as skin-sensitising potency. Risk assessment requires the combination of sensitising potency with dermal exposure to that skin sensitiser so that the risk to human health can be managed. The processes associated with the risk assessment of contact allergens have been reviewed in several recent occasions [1, 2], so a primary focus in the present material will be on the more recent developments, as well as on how the feedback from dermatology clinics informs us on the performance (i.e. success or failure) of the risk assessment.
7.2
Hazard Identification and Characterisation
Predictive test methods and their protocols, advantages and disadvantages generally fall outside the scope of the material here, with thorough reviews being readily available which document progress over several decades (e.g. [3, 4]). Nevertheless, some key points must be addressed. The earliest predictive assays for the identification of chemical skin sensitisation hazards involved the use of a range of guinea pig models (detailed in [3]). All employed a variety of p rocedures over a period of 2–3 weeks which endeavoured to induce sensitisation to the test chemical. The success of 57
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this was then revealed 1–2 weeks later by dermal challenge with the same substance. Test concentrations depended on the irritancy potential of the substance, with the consequence that irritant substances would be evaluated at much lower concentrations than tho
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