What Is Considered a Fever? Causes & Treatment

For body systems to function properly, billions of chemical processes occur to create hemostasis, which is the state of balance within our bodies. Most of those chemical reactions need the optimal temperature to occur. That is why temperature is under the very strict control of many nervous and hormonal mechanisms. Any alteration of those mechanisms can cause a rise or a drop in body temperature. Such change is never normal and can mean anything from a mild infection to a severe life-threatening condition.

What is a fever?

One of the common misconceptions regarding human body temperature is that it is a constant number – usually 37 Celsius or 98.6 Fahrenheit-. Generally speaking, there is never a single value for any vital measurement, be it the heart rate, temperature, blood pressure, or even laboratory values. The reason behind this is the wide variation of internal and external environments of the human body. To counter that, we usually place a normal range for such values, and for temperature, this value ranges from 36.5–37.5 °C or 97.7–99.5 °F.

There is no reason to worry if your temperature is within this range. Reasons as to why your temperature can “swing” within those values include:

  • Age: Age can be a factor owing to the difference in the level of activity, muscle mass, and intolerance to rapid external temperature change.
  • Sex: Women and men differ widely in their muscular build.
  • Female monthly cycle: Female menstrual cycle is a major contributor to monthly temperature changes (about half a degree difference). This results from the fluctuation of the levels of female sex hormones (estrogen and progesterone).
  • Level of activity
  • External temperature: No matter how effective your sweating or muscular structure are, your temperature is likely to be affected by outside cold or heat.

If your temperature rises above this normal range, it is called fever and is classified into three grades:

  • Low-grade fever: 99.5-100.5 °F.
  • Moderate fever: 100.6-103.5 °F.
  • High-grade fever: 103.5-105 °F.
  • Hyperpyrexia: >105 °F: Hyperpyrexia is the most severe and is considered life-threatening unless immediate action is taken to protect the brain against such a high temperature.