Normal body temperature varies with age, activity and time of the day and the average normal body temperature is 37 degrees C. Body temperature varies less in adults, but a woman’s menstrual cycle can elevate body temperature by 1 degree C or more. In children between 6 months to 2 years, the average variation is about 1 degree C and the difference is about 2 degrees C when they become six years old.

A rectal temperature up to 38 degrees C may be entirely normal and above 38 degrees C should be considered a fever. Fever is not a disease and it is an important part of the body’s defence against infection. Fever signals us the fight which is going on in the body against the bacteria or virus or other micro-organisms for your survival. Optimum temperature for bacteria and viruses are 37 degrees C and increasing the temperature few degrees activate the body’s immune system to make more white blood cells and antibodies to fight against.

Brain damage is possible if the fever is above 42 degrees C and untreated fever caused by infection in children go seldom above 40.5 degrees C.

The other causes of fever are including cancers, autoimmune diseases like rheumatoid arthritis or toxins.

In cases where the body cannot stop the rise of temperature such as a child in a hot car or too much of exercise with less fluid intake can cause heatstroke which is very dangerous.