The cause of a fever of 38.5°C in infants is rather complex. First of all, the more common cause is the occurrence of viral or bacterial infections, the most common is the occurrence of upper respiratory tract infection, which is usually called the cold, when there is a cold, there will often be inflammation of the upper respiratory tract, the body will be infected with bacteria or viruses, these bacteria or viruses will secrete a large number of toxins, stimulating the thermoregulatory center, resulting in fever conditions. Anti-infection treatment is often important at this time, for example, bacterial infections can be treated with antibiotics, and the child can be given oral pediatric cefixime granules. If it is a viral infection, you can use antiviral drugs, such as the Four Seasons Antiviral Combination or Pudilan Anti-inflammatory Oral Liquid. In addition, there may be a gastrointestinal infection, such as abdominal pain or diarrhea, there will be absorption of fever, you need to give your child anti-diarrheal drugs, Similac effect is relatively good, and relatively few side effects.