Concerns have been raised that diacetyl (DA) might be a respiratory sensitizer based on its LUMO energy similar to that of the respiratory allergen toluene-2,4-diisocyanate (TDI) and results of a local lymph node assay (LLNA) that reported an EC3 of 1.9%. To better understand the concerns, we performed a systematic literature review and experimental competition reactions between DA and TDI. The experimental evidence demonstrates that DA is at least 400-fold less reactive than TDI. The literature review finds evidence that the EC3 for DA is actually >11%. We conclude that DA is unlikely to have significant respiratory sensitization potential.

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