Biological therapies have revolutionized medical treatment by targeting the key mediators or receptors involved in inflammatory responses, thereby effectively suppressing inflammation and achieving beneficial outcomes. They are more advanced than conventional therapies using corticosteroids and immunosuppressants, offering effective solutions for autoimmune diseases, cancer, transplant rejection, and various infectious diseases, including coronavirus disease 2019. Although they exert low immunosuppressive effects, biological therapies can reactivate specific biological targets associated with infections. This review summarizes the currently available biological therapies and discusses their immunosuppressive mechanisms and clinical applications, highlighting the variations in the types and frequencies of infection recurrence induced by different biological agents. Additionally, this review describes the risk factors associated with various biological agents, thus aiding clinicians in selecting the most appropriate biological therapy.