IL33 and Recurrent upper respiratory tract infections: We believe they may be involved in the following mechanisms: (1) The incidence of upper respiratory tract infections and exposure to outdoor allergens and contaminants decreased significantly during the COVID-19 pandemic, while it has been documented that viral respiratory pathogens, such as rhinoviruses and respiratory syncytial viruses, augment the induction of airway epithelia to secrete pro-T helper 2 cytokines, namely TSLP, IL-25, and IL-33, which facilitate the occurrence of sensitization [20].