Functional fever is a low fever caused by non-organic infections, usually with a body temperature below 38°C, accompanied by clinical symptoms and manifestations such as excessive sweating and fatigue, with a body temperature between 37.3 and 38°C, and lasting for more than 2 weeks. The diseases that cause functional fever are as follows: First, chronic infections, such as tuberculosis, connective tissue disease, rheumatism, and fever caused by rheumatism, can be called functional fever. Second, anemia, malignant tumors, hyperthyroidism, and systemic lupus erythematosus-like connective tissue diseases can also cause functional fever. Thirdly, during the ovulation period of women, the body temperature will be higher than normal by about 0.3℃, which is also called functional fever.