Fever (also known as pyrexia or controlled hyperthermia) is when a human's body temperature goes above the normal range of 36-37C (98-100F) - it is a common medical sign.
As the individual's body temperature goes up, there may be a sensation of cold until the temperature plateaus (stops rising).
People's normal body temperatures may vary and are affected by factors such as eating, exercise, sleeping and what time of the day it is. Our body temperature is usually at its highest at around 6pm and at its lowest at about 3am.
An elevated body temperature (fever) is one of the ways our immune system attempts to combat an infection. Usually the rise in body temperature helps the individual resolve an infection. However, sometimes it may rise too high, in which case the fever can be serious and lead to complications.
Physicians say that as long as the fever is mild, we do not generally need to try and bring it down - if the fever is not severe it is probably having an effect in neutralizing the bacterium or virus that is causing the infection. Medications to bring down a fever are called antipyretics. If the fever is causing undue discomfort, an antipyretic may be recommended. US and UK doctors say that when the fever reaches or exceeds 38ºC (100.4ºF) it is no longer mild and should be checked a couple of hours later.
The temperatures mentioned above are when they are taken in the mouth. For normal armpit temperatures, you need to reduce those numbers by about 0.2ºC to 0.3ºC.
Symptoms of fever
A symptom is something the patient reports and feels, while a sign is something other people, including a doctor may detect. For example, a headache may be a symptom while a rash may be a sign.
When somebody has a fever, signs and symptoms are linked to what is known as sickness behavior, and may include:
A person is said to have a fever if the temperature in the mouth is over 37.7C (99.9F). Temperature can also be measured in the rectum (anus), under the arm or inside the ear.
- Feeling cold when nobody else does
- Anorexia - lack of appetite
- Dehydration - preventable if the patient drinks plenty of fluids
- Hyperalgesia - the individual is much more sensitive to pain
- Problems concentrating
If the fever is high there may also be extreme irritability, confusion, delirium and convulsions.
Febrile seizure (children)
Children with a high temperature may develop a febrile seizure, also known as a febrile fit or febrile convulsion, most of which are not serious and may be the result of an ear infection, gastroenteritis, or a respiratory virus (a cold). Less commonly, febrile seizures may be caused by something more serious, such a meningitis, a kidney infection or pneumonia.
Febrile seizures most commonly occur in children aged 6 months to 6 years, and affect boys more often than girls.
The seizure occurs because the body temperature rises too fast, rather than because it has been sustained for a long time.
There are two types of febrile seizures:
1) Simple febrile seizure - the seizure lasts no longer than 15 minutes (in most cases less than 5 minutes) and does not occur again during a 24-hour period.
It typically involves the whole body - a generalized tonic-clonic seizure. Most febrile seizures are of this type. Symptoms - the body becomes stiff and the arms and legs start to twitch, the patient loses consciousness (but the eyes stay open).
There may be irregular breathing and the child may urinate and/or defecate. There may also be vomiting.
2) Complex febrile seizure - the seizure lasts longer, comes back more often, and tends not to affect the whole body, but rather only part of the body.
This type of seizure is a cause for more concern that simple febrile seizures.
In the majority of cases, a child with a febrile seizure does not need treatment. Temperature may be controlled with acetaminophen (paracetamol) or sponging. If necessary an anticonvulsant, such as sodium valproate or clonazepam may be prescribed.
Causes of fever
- An infection - such as strep throat, flu, chickenpox or pneumonia
- Rheumatoid arthritis
- Some medications
- Over-exposure of skin to sunlight (sunburn)
- Heat stroke - may be caused either by exposure to high temperatures (nonexertional heat stroke) or prolonged strenuous exercise.
- Silicosis - a type of lung disease caused by long-term exposure to silica dust.
- Amphetamine abuse
- Alcohol withdrawal
On the next page we look at how to diagnose a fever, treatments for fever and fever prevention.