It is more common to have a fever for four days in a row. There are indeed many causes of fever, and it is important to find out the specific cause of fever to carry out targeted treatment for better results. The causes of the occurrence are divided into two main areas: first, it is caused by infectious causes, such as respiratory infections, urinary system infections, endocarditis or viral encephalitis, all of which may result. It often requires a visit to the hospital for a specific examination to clarify. Secondly, there are also many non-infectious factors, more commonly connective tissue diseases, such as rheumatoid arthritis or systemic lupus erythematosus, which can easily lead to continuous fever. Thirdly, relatively rare tumors may also cause it, and it is necessary to go to the hospital for screening of tumor factors is also very necessary. So finding the cause of the fever for targeted treatment is the most important measure to reduce the fever.