Issues and challenges around classification of respiratory sensitizers/allergens in the United Nations Globally Harmonized System

Introduction

The United Nations Globally Harmonized System (GHS) of classification and labelling provides specifications for the classification, management, and communication of hazards, crucial for protecting workers and consumers. However, issues and challenges exist in its application, particularly concerning respiratory sensitizers, many of which can become airborne pollutants in occupational settings and in broader environments, where they may engulf entire regions.

Methods

This is a narrative review that assesses relevant GHS documents and internationally accepted methods for determining respiratory sensitizers.

Results

Chemical sensitization is complex and depends on factors like allergen nature, dose, and exposure route, including inhalation. Sensitization initially involves the induction of specialized immunological memory in an individual by exposure to an allergen, followed by elicitation, which is the production of an allergic response following exposure of a sensitized individual to an allergen. Consequently, predictive tests also involve both induction and elicitation, followed by classification as Category 1, 1A or 1B, depending on the evidence. Unfortunately, GHS classification relies heavily on epidemiological data captured retrospectively with diagnostic testing rather than on prospective (predictive) data. Moreover, there are issues regarding the potency of chemicals and absence or presence of no-adverse-effect levels (NOAELs). Accurately assessing airborne exposure to sensitizers can be challenging, especially in complex environments, making it difficult to establish clear dose–response relationships. Lastly, the potential for certain respiratory sensitizers to become airborne and persist in the atmosphere increases the risk of prolonged inhalation exposure, underscoring the necessity for accurate GHS classification.

Conclusion

Challenges exist in interpreting results and accurately classifying sensitizers, potentially underestimating risks associated with airborne exposure. Users of GHS SDSs and labels must be aware of these limitations, particularly concerning inhalation exposure and potential airborne pathways. Further research is needed to improve GHS classification and understanding of the atmospheric behavior of sensitizers.