Potency values from the local lymph node assay: application to classification, labelling and risk assessment

Area of Science:

• Toxicology
• Dermatology
• Chemical Safety

Background:

• Contact allergens pose significant hazards, necessitating accurate identification and characterization.
• Existing methods for assessing skin sensitization require refinement for classification and risk assessment.

Purpose of the Study:

• To evaluate the local lymph node assay (LLNA) for defining threshold criteria (EC3 values) for classification and labeling.
• To reassess existing recommendations for sub-categorizing substances based on potency.
• To provide recommendations for classifying and labeling preparations under the Globally Harmonized System (GHS).
• To integrate LLNA data into quantitative risk assessment strategies.

Main Methods:

• Review of the local lymph node assay (LLNA) and its application in determining EC3 values.
• Analysis of concentration-response data for skin sensitizing chemicals.
• Evaluation of existing frameworks for classifying contact allergens by potency.

Main Results:

• Currently, an EC3 value below 100% cannot be reliably defined as a threshold for classification and labeling.
• A four-category system ('extreme', 'strong', 'moderate', 'weak') is proposed as the most appropriate science-based classification for contact allergens based on potency.
• LLNA EC3 values are suitable for determining a no expected sensitization induction level, a key step in quantitative risk assessment.

Conclusions:

• The LLNA is a valuable tool for assessing skin sensitization potency.
• A refined, multi-category classification system based on LLNA data improves the scientific basis for hazard characterization.
• LLNA data integration into risk assessment provides a quantitative approach to managing skin sensitization risks.