Although homeotherms maintain a stable core body temperature through the coordinated regulation of multiple physiological systems, various factors can still lead to abnormal body temperature. While the immune-enhancing effects of fever are well understood, research on how low body temperature regulates immunity remains limited. Notably, cold therapy and hypothermia have been used to manage various diseases, including neurological and metabolic disorders. This review provides a comprehensive overview of the causes of hypothermia, its modulatory effects on immunity and underlying mechanisms, and its therapeutic applications in clinical diseases.