Percent amino-acid identity thresholds are not necessarily conservative for predicting allergenic cross-reactivity

International guidance on assessing amino-acid sequences for allergenic cross reactivity, such as that provided by Codex, relies on percent amino-acid identity across local alignments. Previous work has shown this approach to exhibit poor selectivity for true allergen cross-reactivity. Here we provide a hypothetical example illustrating that this approach is also not necessarily conservative in detecting high similarity across amino acid sequences, and thus, is not necessarily conservative in detecting potential allergenic cross reactivity among proteins. It is recommended that an established local-alignment bioinformatic tool like FASTA be used in conjunction with statistical measures of similarity to detect the risk of a protein cross-reacting with an allergen.