User Guide to Thresholds and Classification - Environmental ...

195User Guide for Thresholds and Classifications13. Respiratory or Contact Sensitisation – Subclass 6.513.1. General considerations13.1.1. Respiratory or contact sensitisationSee section 9.6 in chapter 9 for definitions of the key terms used in this chapter.Sensitisation includes two phases: the first phase is the induction of specialised immunological memory in anindividual by exposure to an allergen; the second phase is the production of a cell-mediated or antibodymediatedresponse by a sensitised individual exposed to an allergen that is sufficient to elicit the response.This two-phase process applies to both respiratory and contact sensitisation.For contact sensitisation, an induction phase is required in which the immune system learns to react. Clinicalsymptoms can then arise when subsequent exposure is sufficient to elicit a visible skin reaction (theelicitation phase). As a consequence, predictive tests usually follow this pattern in which there is an inductionphase, the response to which is measured by a standardised elicitation phase, typically involving a patchtest. The local lymph node assay, which directly measures the induction response, is the exception.Evidence of contact sensitisation in humans normally is assessed by a diagnostic patch test.Usually, for both contact and respiratory sensitisation, lower levels are necessary for elicitation than arerequired for induction.13.1.2. Sensitisation by other routesSensitisation may occur through routes other than through contact or respiratory exposure (for example,photosensitisation or oral ingestion causing sensitisation). At this stage, sensitisation through these routeswill not trigger a 6.5 classification. However, when the Hazardous Substances (Minimum Degrees of Hazard)Regulations 2001 and Hazardous Substances (Classification) Regulations 2001 are reviewed, the criteria forclassifying substances as sensitisers may be revised to capture substances that cause sensitisation throughroutes other than contact and respiratory sensitisation.PhotosensitisationPhotosensitisation reactions may occur when a substance absorbs ultra-violet (UV) or visible light.Photosensitisation includes:photo-irritation, which is a light-induced skin response to a photo-reactive chemical; andphoto-allergy, which is an immunologically mediated reaction to a chemical initiated by the formation ofphoto-products (for example, the photo-products produce an antigen).Substances that cause photosensitisation (for example, halogenated aromatic hydrocarbons or sunscreenagents can cause photo-contact allergy) should not be classified under subclass 6.5. Photosensitisation isnot considered an intrinsic property of a substance as an external stimulus is required (for example, UV orvisible light).January 2012 EPA0109