It is not normal to have a fever followed by a cold, suggesting that the body is invaded by viruses, bacteria, mycoplasma, chlamydia, rickettsia and other pathogens, and the inflammatory reaction occurs in the respiratory mucosa with congestion, edema and exudation of inflammatory substances. At this time, the immune system in the body is active, causing the body to produce a large number of endogenous pyrogens, and the body temperature fluctuates, or even tends to gradually climb. Blood tests can be performed to identify the cause and treat the symptoms and cause. Drink more warm water, urinate and sweat to take away body heat and achieve the purpose of lowering body temperature. Acetaminophen or ibuprofen can be used to reduce fever when the body temperature exceeds 38.5°C or more. Anti-pathogen treatment, such as anti-viral can use drugs such as ribavirin and oseltamivir.