 While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease.The early phase of the allergic reaction typically occurs within minutes, or even seconds, following allergen exposure and is also commonly referred to as the immediate allergic reaction or as a Type I allergic reaction.The reaction is caused by the release of histamine and mast cell granule proteins by a process called degranulation, as well as the production of leukotrienes, prostaglandins and cytokines, by mast cells following the cross-linking of allergen specific IgE molecules bound to mast cell FcεRI receptors.