Unexplained hypothermia is usually called nameless fever and usually results from three major categories of causes: i. Infectious hypothermia includes bacterial infections, viral infections, fungal infections and infections from other atypical pathogens, such as respiratory tract infections, biliary tract infections or diseases such as chronic pyelonephritis, chronic urinary tract infections, and chronic pelvic inflammatory disease can produce hypothermia. Second, non-infectious inflammatory reactions, such as rheumatic diseases, rheumatoid diseases, immune tissue diseases, connective tissue diseases, and tuberculosis type diseases can also produce unexplained hypothermia. Third, diseases caused by common factors of endocrine hypofunction, such as hypothyroidism and adrenal insufficiency can also present with unexplained hypothermia. Rare diseases can also present with unfixed fever, such as severe anemia, tumors, and AIDS can also present with the above clinical symptoms.