Overview Summary of Available Evidence for Methyl Methacrylate

The available clinical and experimental evidence does not scientifically justify classifying Methyl Methacrylate (MMA) as a respiratory sensitiser, suggesting the Risk Assessment Committee (RAC) opinion should not be ratified. The data indicates that MMA acts as a respiratory irritant rather than an immune-mediated sensitiser. 

Clinical Evidence and Limitations

The CLP framework requires distinguishing new-onset occupational asthma (relevant for classification) from work-exacerbated asthma. The clinical data relied upon by the RAC contains major limitations: 

• Specific Inhalation Challenge (SIC) Tests: The RAC relied on four positive SIC tests, but these pre-date modern 2014 European Respiratory Society (ERS) guidelines. They lack critical documentation (medical histories, spirometry data, placebo controls) and failed to monitor exposure, likely exposing subjects to irritant-level concentrations. Furthermore, three tests involved complex mixtures, making direct attribution to MMA impossible. Confidence is further lowered by a subsequent series of 16 SIC tests on MMA products that were all entirely negative. 

• Walters et al. (2017) Case Studies: Out of the cases reviewed, the RAC itself concluded they were insufficiently reliable. One worker was co-exposed to MDI (a known sensitiser), meaning MMA may have simply triggered work-exacerbated asthma. Another case involving bone cement was likely a sensitisation to gentamycin sulphate, with MMA acting merely as an irritant. 

• National Surveillance Data: While useful for tracking trends, surveillance data lacks the diagnostic precision required for chemical classification because it is unable to separate occupational asthma from work-exacerbated asthma and lacks transparency as to the basis of attribution. 

New Approach Methodology (NAM) Data

Modern mechanistic (NAM) data strongly supports the view that MMA is an irritant rather than a sensitiser and should be used to reduce regulatory uncertainty: 

• Recent studies show negative findings for three out of four key events in the Adverse Outcome Pathway (AOP 39) for respiratory sensitisation. 

• Testing on human lung tissue models showed no relevant gene activation. 

• This data indicates MMA lacks the intrinsic biological properties required to cause immune-mediated respiratory sensitisation. 

More comprehensive analysis of these claims is detailed in the supporting files.

• Summary of Specific Inhalation Challenge SIC Cases

  • Details on SIC cases

  • SIC Tests Exposure Levels

  • Delayed Asthmatic Responses in SIC Tests

  • Publications

• Co-Exposure Aspects

• Case Analysis - Walters 2017

• Summary of National Health Databases

  • Details of National Health Databases

• Summary of Mechanistic Data on Immune Reaction

  • Mechanistic data Fulfil Sound Scientific Principles

  • Publications & EFSA