What constitutes and causes a fever?

What constitutes a fever?

A rectal temperature greater than 100.5 degrees Fahrenheit or 38 degrees Celsius is considered a fever. Most children have a normal oral body temperature of 98.6 degrees Fahrenheit or 37.5 degrees Celsius, but normal temperature varies among children from 97 to 100 degrees Fahrenheit or 36.1 to 37.8 degrees Celsius. Rectal temperature registers about one degrees higher than oral temperature. Many children show normal daily fluctuations in body temperature. It can be lower in the morning and during the rest and a degree higher in the late afternoon or during strenuous exercise.

What causes a fever? 

Fever is symptom of an underlying illness, but it is not an illness itself. A fever occurs when more heat is produced in the body than can be released, thus raising your child's temperature. Germs from infection within your child's body release substances into the bloodstream called pyrogens, which cause the fever.

Normal body temperature is maintained by a thermostat in a tiny organ of the brain called hypothalamus, which regulates the balance between the heat produced and the heat lost in the body. Anytime there is a change from normal body temperature, the thermostat reacts to help the body bring that temperature back to normal; for example, when your child is cold, she shivers to produce heat. When your child has a fever, the blood vessels of her skin become larger as evidenced by her flushed cheeks, and her heart beats faster. These mechanisms cause more blood to reach the surface of the skin to release the excess body heat. A child with fever also sweats to cool her body by evaporation and breathes faster to get rid of body heat through the warm air she exhales. In addition to having these general signs of fever, a child may have headaches and fatigue.