Medical Articles

Understanding Fever (Part 1)

05.05.2026

When a child falls ill, fever is often the symptom that causes parents the most anxiety. It’s perfectly natural to feel worried when your child’s temperature rises. Over the next few articles, we will focus on fever—the most common symptom in children—to help you understand when to seek medical care and how to provide effective home care.

Fever is the most frequent reason for pediatric visits. Some reports estimate that fever accounts for 30% of the symptoms seen by pediatricians. However, while common, there are surprisingly many misconceptions about it.

First, what exactly is defined as "having a fever"? According to Japanese medical standards, a "fever" is defined as a body temperature of 37.5°C or higher, and a "high fever" as 38.0°C or higher. In a survey of approximately 600 parents asking, “At what temperature would you consider taking your child to a doctor?” the most common response was 38.0°C or higher (27%), followed by 38.5°C and 39.0°C (21% each). Only 3% said they would visit for a temperature of 37.5°C. This suggests that 38.0°C is a common threshold for parents.

It is also important to note that human body temperature fluctuates throughout the day, tending to be lower in the morning and higher in the evening. Therefore, even if a child’s temperature seems low in the morning after having a fever the previous day, sending them to daycare or school requires caution, as the fever may often return in the afternoon.

In the next article, we will discuss how to handle a fever when it occurs.

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