In contrast, hyperthermia involves body temperature rising above its set point due to outside factors. The high temperatures of hyperpyrexia are considered medical emergencies, as they may indicate a serious underlying condition or lead to severe morbidity (including permanent brain damage), or to death. A common cause of hyperpyrexia is an intracranial hemorrhage. Other causes in emergency room settings include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug overdose, serotonin syndrome, and thyroid storm. Differential diagnosis
Fever is a common symptom of many medical conditions:

Infectious disease, e.g., COVID-19, dengue, Ebola, gastroenteritis, HIV, influenza, Lyme disease, rocky mountain spotted fever, secondary syphilis, malaria, mononucleosis, as well as infections of the skin, e.g., abscesses and boils. Immunological diseases, e.g., relapsing polychondritis, autoimmune hepatitis, granulomatosis with polyangiitis, Horton disease, inflammatory bowel diseases, Kawasaki disease, lupus erythematosus, sarcoidosis, and Stills disease;
Tissue destruction, as a result of cerebral bleeding, crush syndrome, hemolysis, infarction, rhabdomyolysis, surgery, etc. ;
Cancers, particularly blood cancers such as leukemia and lymphomas;
Metabolic disorders, e.g., gout, and porphyria; and
Inherited metabolic disorder, e.g., Fabry disease.Adult and pediatric manifestations for the same disease may differ; for instance, in COVID-19, one metastudy describes 92.8% of adults versus 43.9% of children presenting with fever.In addition, fever can result from a reaction to an incompatible blood product.Teething is not a cause of fever. Function
Immune function
Fever is thought to contribute to host defense, as the reproduction of pathogens with strict temperature requirements can be hindered, and the rates of some important immunological reactions are increased by temperature.
: 103  Hyperthermia is not to be confused with hyperpyrexia (which is a very high fever). : 102 Clinically, it is important to distinguish between fever and hyperthermia as hyperthermia may quickly lead to death and does not respond to antipyretic medications. The distinction may however be difficult to make in an emergency setting, and is often established by identifying possible causes. : 103

Types
Various patterns of measured patient temperatures have been observed, some of which may be indicative of a particular medical diagnosis:
Continuous fever, where temperature remains above normal and does not fluctuate more than 1 °C in 24 hours (e.g. in bacterial pneumonia, typhoid, infective endocarditis, tuberculosis, or typhus. Intermittent fever is present only for a certain period, later cycling back to normal (e.g., in malaria, leishmaniasis, pyemia, sepsis, or African trypanosomiasis. Remittent fever, where the temperature remains above normal throughout the day and fluctuates more than 1 °C in 24 hours (e.g., in infective endocarditis or brucellosis). Pel–Ebstein fever is a cyclic fever that is rarely seen in patients with Hodgkins lymphoma. Undulant fever, seen in brucellosis. Typhoid fever is a continuous fever showing a characteristic step-ladder pattern, a step-wise increase in temperature with a high plateau.Among the types of intermittent fever are ones specific to cases of malaria caused by different pathogens.