The number of patients with allergic diseases (hay fever, food allergy, atopic dermatitis) is increasing worldwide. These are caused by allergens (pollen, food, environmental substances) that activate IgE receptors (FcεRI) on mast cells by allergen-specific IgE, resulting in the secretion of inflammatory mediators (histamine) (Figure below). Allergic diseases are regulated by various factors (stress, aging, environmental substances). Here, we are examining the causes of allergic diseases to develop treatments.