There are many reasons why adults have recurring fevers after a cold, and the main reasons may include insufficient time to administer medication after a cold, failure to target pathogens, or comorbidities with other illnesses such as blood system disorders. 1. Insufficient medication time: Generally, there is no need to take medication for minor colds. If the symptoms of a cold are severe or the cold is combined with a bacterial infection, and the temperature drops after antiviral or antibiotic medication is used against the pathogen, but the temperature rises again after the medication is discontinued, then the duration of the medication is often insufficient. 2. Not targeting specific pathogens: the use of drugs is not appropriate, just use some fever-reducing drugs, but these fever-reducing drugs can only play an auxiliary therapeutic role, is the treatment of the symptoms rather than the root cause, it does not address the pathogens that cause disease, the body temperature is down is also temporary, and will be elevated again. 3. Combined with other diseases: such as blood system disease lymphoma, or immune system diseases such as rheumatic diseases. If there is no significant improvement in fever after a long period of time, you should go to the hospital as soon as possible to find out the cause of the illness, so as not to delay the condition.