Fever is an illness that can cause heatstroke. A person with a high fever is usually suffering from a serious illness or injury, or is at an increased risk for serious illness or death.

Fever can be caused by a viral, bacterial, fungal, or viral infection. The most common causes of fever are infections, especially those that are handled by the body's immune system. Common infections include colds, coughs, upper respiratory tract infections, sinus infections, and urinary tract infections. A fever may also result from other causes, including some types of cancer and heart disease.

How to Measure Fever

A fever is measured by using a thermometer to measure body temperature. The most accurate thermometers measure temperature in degrees Celsius (°C), whereas most digital thermometers in mobile devices measure temperature in Fahrenheit (°F).

If the temperature is above 37.5 °C (.5 °F), you may experience cold or pain in your muscles.