Adult fever of 38.5℃ is a moderate fever, which has a more serious effect on the organism, but whether it is dangerous or not is not judged by temperature alone, but also needs to be combined with other symptoms and auxiliary examinations for systematic analysis and treatment. In adults, a fever of 38.5°C is mostly caused by infectious diseases, such as the flu, and may result in dizziness, headache, nausea, vomiting, peripheral weakness, muscle aches and pains, etc. This period should be treated actively to prevent further aggravation of the condition. Physical cooling as well as fever-reducing medications such as ibuprofen and acetaminophen can usually be given. If no medication is given or other methods are not sought to reduce fever, it can easily cause hyperthermia as well as affect the person’s central nervous system and cause damage to internal organs. At the same time, blood tests are performed to clarify the type of infection. If it is caused by a viral infection, it can be treated without special treatment and can get better on its own after a week. If it is caused by bacterial infection, it needs to be treated with sensitive and reasonable antibiotics. In addition, some non-infectious diseases, such as rheumatic immune diseases, connective tissue diseases, hyperthyroidism, tuberculosis and other oncological diseases, can also cause fever of 38.5℃ in adults, which may be dangerous if not treated in time. Therefore, adults with fever of 38.5℃ should be alerted to the specific cause and actual condition for systematic and standardized diagnosis and treatment to avoid life-threatening consequences.