The Basic Law on Measures against Allergic Diseases in Japan was enforced on December 25, 2015. Six diseases are defined as allergic diseases: bronchial asthma, atopic dermatitis, allergic rhinitis, allergic conjunctivitis, pollinosis (hay fever), and any food allergy. All of these are reported to be strongly associated with type 2 immune responses, in which conventional and pathogenic type 2 helper T (Th2) cells play important roles (Nakayama et al., 2017) (Kokubo et al., 2022). Topical agents and/or medications, including antihistamine, antileukotriene, thromboxane inhibitors, and corticosteroids, are the standard treatment for allergic diseases (Nagai, Teramachi, & Tuchiya, 2006). However, these traditional approaches have limited clinical efficacy. Therefore, there is a need for new therapeutic agents (Yang, Kambe, Takimoto-Ito, & Kabashima, 2021). Emerging findings on the pathogenesis of allergic diseases, particularly those mediated by pathogenic Th2 cells, are advancing with the development of novel and promising treatments. In this review, we provide an overview of therapeutic biologics and small molecules for preventing the functions of Th2 cells. This review also discusses new insights on the mechanisms underlying allergic disease.