An assessment of how likely a food, ingredient, or novel protein is to cause allergic reactions, a formal step in the safety evaluation of genetically modified foods and new protein sources. Regulators examine whether the introduced protein resembles known allergens in its amino acid sequence, whether it resists digestion in simulated gastric fluid, since stable proteins are more likely to sensitize, and whether it binds antibodies from the blood of allergic patients. A finding of significant similarity to a known allergen can halt a product’s development, as happened with a Brazil-nut gene once proposed for soybeans. The concept also guides labeling decisions and the design of hypoallergenic formulas. As novel proteins from insects, algae, and precision fermentation enter the food supply, allergenic potential assessment is becoming one of food safety’s busiest frontiers.