If there is no cough or runny nose but only fever, we can only exclude fever caused by common upper respiratory tract infection, but there are many causes of fever and specific tests are needed to clarify them. The causes of fever are divided into infectious and non-infectious factors. If the fever is caused by an infection, it may be a bacterial infection or a viral infection, or it may be caused by mycoplasma, chlamydia, mycobacterium tuberculosis or other infectious diseases, so a specific examination is necessary. In addition, non-infectious factors may also lead to fever, such as blood system diseases that often induce fever; rheumatic immune system diseases, such as systemic lupus erythematosus, may also lead to fever; endocrine diseases may also lead to abnormal body temperature, so the causes of fever are very many.