The body will suddenly get hot including physiological factors (activity, hormone level changes, etc.), infectious factors (bacterial infection, fungal infection, etc.) and non-infectious factors (connective tissue disease, diseases caused by low immunity, etc.). 1. Physiological factors: including body fever after strenuous exercise and fever caused by changes in hormone levels during menstruation. 2. Infectious factors: including bacterial infections, fungal infections, viral infections, and atypical pathogen infections (mycoplasma, chlamydia, etc.), the above pathogens lead to infections of the respiratory tract, gastrointestinal tract, urinary tract and other parts of the body, which can lead to sudden fever. 3. Non-infectious factors: including connective tissue diseases, diseases caused by low immunity, metabolic diseases, such as systemic lupus erythematosus, rheumatoid arthritis, AIDS, tumors, hyperthyroidism, menopausal syndrome, etc., all of which can lead to sudden onset of fever. Whatever the cause of sudden onset of fever, it is necessary to closely monitor changes in body temperature, and if necessary, consult a hospital in time to avoid delaying the condition.