Food allergies are IgE-mediated immunological reactions; this distinguishes them from other adverse reactions to foods. Most (>90%) of the recognized food allergies are generally thought to be caused by eight foods or food groups. A number of factors can affect food allergy development, including diet and culture, route of exposure, processing, cooking, and digestion. In addition, it is thought that the properties of certain food proteins render them more likely to be allergenic than other proteins. Most food allergens are major proteins, polyvalent molecules with at least two or more IgE-binding sites, and are recognized as foreign molecules (hence immunogenic). A number of major food allergens have been recently characterized, and amino acid sequences determined. Tropomyosin is the only major allergen of shrimp. A number of IgE-binding epitopes have been identified in this molecule, though they may vary from one shrimp-allergic individual to another. Single amino acid substitutions within epitopes based on that of homologous, nonreactive tropomyosins can substantially enhance or abolish IgE antibody binding. Using the accumulated knowledge of food allergen protein structure, the allergenicity of novel proteins to which there has been no prior human exposure has been assessed. This has been based primarily on the lability or resistance of a protein to enzymatic degradation. Clearly, further criteria must be developed to refine this process. In this regard, the development of animal models that have been sufficiently validated as surrogates of human IgE antibody responses is needed for more precise assessment of the allergenic potential of proteins.