This paper is a review concerning the way in which heat treatment can modify the allergenicity of food proteins. Any food protein may be allergenic if it can be absorbed intact, or as substantial fragments, through the gut mucosa and then evoke an immune (allergic) response. The intrinsic properties of the protein, the overall composition of the food, and the past processing history (especially thermal processing) all have an effect on the allergic potential. When a protein is denatured by heat, most of the original tertiary structure is lost, so that many of the sites recognized by antibodies on the native molecule are destroyed. There are many examples of allergenicity being reduced, but not eliminated, by heating. But heat-denatured proteins can also present new antigenic sites, uncovered by the unfolding process or created by new chemical reactions with other molecules present in the food (e.g., β-lactoglobulin associating with a-lactalbumin in milk). We have found that heat-denatured β-lactoglobulin has at least one new epitope, not found in the native state. Therefore, thermal processing can be part of a procedure for making hypoallergenic food, but will rarely be sufficient on its own. Increased understanding will help in evaluating novel proteins and processes.