What Is It?
A fever is an increase in body temperature above the normal range. However, body temperature varies between people, with different levels of activity and at different times of the day. Medical textbooks differ in their definition of the highest normal body temperature. Fever generally can be defined as an early morning temperature higher than 99 degrees Fahrenheit or a temperature higher than 100 degrees Fahrenheit at any time of the day.
A part of the brain called the hypothalamus acts as the body's thermostat. When all is well in the body, the hypothalamus is set at the normal body temperature. Fever develops when the hypothalamus is set to a higher-than-normal temperature. This resetting of the hypothalamus is usually caused by small molecules called pyrogens in the blood. Pyrogens can come from outside the body (external) or can be produced inside the body (internal). External pyrogens include toxins (poisons) produced by infectious viruses or bacteria. Internal pyrogens include abnormal chemicals that are produced by tumors and proteins that are released during the normal response of the immune system.
Causes of fever include:
Common symptoms associated with fever include sweating, shivering, headaches, muscle aches, poor appetite, rash, restlessness and general body weakness. High fever can lead to symptoms of mental dysfunction, such as confusion, excessive sleepiness, irritability and convulsions (seizures).
Convulsions triggered by fever (febrile seizures) are common among children younger than 5 years. These seizures usually occur at the beginning of an illness when temperature rises rapidly. In infants and toddlers, febrile seizures typically cause muscle rigidity and generalized convulsions that last less than 15 minutes. A febrile seizure usually is followed by a long period of sleep.
Specific symptoms associated with a fever often can provide clues to help identify the fever's cause. For example, a fever accompanied by vomiting and diarrhea may signal gastroenteritis, and a fever associated with coughing, shortness of breath and grayish-yellow phlegm may indicate pneumonia.
In pinpointing a fever's cause, your doctor may ask about:
Your doctor will take your temperature orally, in the ear canal or rectally. Depending on the suspected site of infection, your doctor may then examine your:
Depending on your symptoms and the results of your physical examination, you may need diagnostic tests, including laboratory examination of body fluids (blood, urine, stool or spinal fluid); special X-rays or scans; or a biopsy (taking a sample of body tissue for laboratory examination).
Depending on its cause, a fever may disappear in a day or last for weeks.
You can reduce your risk of getting illnesses that cause fever by adopting these healthy habits:
Doctors often advise adults with mild to moderate fevers below 102 degrees Fahrenheit to:
Aspirin should not be given to infants and children younger than age 16 because of the risk of Reye's syndrome, a life-threatening neurological disorder that can develop when children take aspirin during a viral illness. In children, reduce fever by using acetaminophen or ibuprofen, together with lukewarm sponge baths. If your child has a febrile seizure, call your doctor immediately.
If your doctor suspects that a bacterial infection is causing your fever, he or she will prescribe antibiotics.
When To Call a Professional
Adults and children should seek immediate medical attention for any fever of 104 degrees Fahrenheit or higher or for any fever accompanied by one or more of the following:
Call a doctor immediately if an infant younger than 3 months develops any fever.
For a lower fever of unexplained origin, call your doctor if it does not improve after two to three days. Call sooner if you develop additional symptoms.
For most fevers caused by common infections, the person either recovers on their own or the doctor is able to identify and treat the cause.
Sustained body temperatures of 106 degrees Fahrenheit or above can cause brain damage.
American Academy of Family Physicians (AAFP)
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