Usually, low fever should not last for 1 week in the body. Low fever within 1 week can be due to viral cold, which can be cured within 1 week without medication. However, if the low fever lasts for more than 1 week, it is necessary to go to the hospital to identify the pathogens and choose the medication for the pathogens for systematic treatment. The causes of low fever are as follows: 1, the most common factors are infectious factors, such as bacteria, viruses, fungi and other pathogenic microorganisms, such as mycoplasma and chlamydia infection of the body, the body will produce endotoxin response, at this time there will be a low fever. 2, some connective tissue diseases can also appear low fever, such as rheumatism, rheumatoid disease, systemic lupus erythematosus, dry syndrome, Dermatomyositis and other diseases, will also appear to have a low fever. 3, in some patients with extremely low immunity, such as tuberculosis, anemia, tumors, AIDS and other conditions, will also appear to have a low fever. Therefore, if the low fever lasts for more than 1 week, it is necessary to go to the hospital to find out the cause.