A fever -- also known as a high fever or a high temperature -- is not by itself an illness. It's usually a symptom of an underlying condition, most often an infection.
Fever is usually associated with physical discomfort, and most people feel better when a fever is treated. But depending on your age, physical condition, and the underlying cause of your fever, you may or may not require medical treatment for the fever alone. Many experts believe that fever is a natural bodily defense against infection. There are also many non-infectious causes of fever.
Fever is generally not considered dangerous, but hyperthermia can cause dangerous rises in body temperature. This can be due to an extreme temperature associated with heat injury such as heat stroke, side effects of certain medications or illicit drugs, and stroke. With hyperthermia, the body is no longer able to control body temperature.
According to the American Academy of Pediatrics, if you have an infant younger than 4 months old with a rectal temperature of 100.4 F or above, you should immediately call your doctor or go to an emergency room, because it could be a sign of a potentially life-threatening infection. Also call your doctor or go to the emergency room if any child has a fever above 104 F. High fever can cause seizures in young children.
Call your doctor right away if your child has a fever and:
Looks very sick
Is drowsy or very fussy
Has a weakened immune system or other medical problems