Food allergy is defined as an immune system-mediated adverse reaction to food proteins. Class 1 food allergens are represented by peanut, egg white, and cow's milk; they are heat- and acid-stable glycoproteins that induce allergic sensitization via gastrointestinal tract and cause systemic reactions. Class 2 food allergens are homologous to proteins in birch tree pollen and class 2 food allergy develops as a consequence of respiratory sensitization to the cross-reactive pollen. Class 2 food allergens are very heat-labile and tend to induce reactions limited to oral allergy symptoms. In contrast, plant nonspecific lipid transfer proteins are resistant to heating and tend to induce systemic reactions. Analysis of IgE-binding epitopes with SPOT membranes revealed that cow's milk-, egg- and peanut-allergic subjects without IgE antibodies against certain sequential epitopes of the major allergens were more likely to achieve tolerance than subjects whose IgE antibodies were directed against those epitopes. Subsequently, peptide microarray showed a correlation between reaction severity and the intensity of IgE binding and the number of epitopes recognized of patients' immune responses against peanut allergens. Taken together, these data suggest that the epitope recognition pattern and intensity of IgE binding are important determinants of severity and duration of food allergy.