Fever is when a human’s body temperature goes above the normal range of 36–37° Centigrade (98–100° Fahrenheit). It is a common medical sign.
Other terms for a fever include pyrexia and controlled hyperthermia.
As the body temperature goes up, the person may feel cold until it levels off and stops rising.
Fevers are common but can be unpleasant.
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 6 p.m. and at its lowest at about 3 a.m.
A high body temperature, or 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.
Doctors say that as long as the fever is mild, there is no need to bring it down – if the fever is not severe, it is probably helping to neutralize 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.
When a fever reaches or exceeds 38° Centigrade (100.4° Fahrenheit), it is no longer mild and should be checked every couple of hours.
These temperatures refer to oral measurement, when the thermometer is put in the mouth. For normal armpit temperatures, the temperature measures lower than it actually is and the numbers are reduced by about 0.2–0.3° Centigrade.
When somebody has a fever, signs and symptoms are linked to what is known as sickness behavior, and may include:
Temperature can be measured in the mouth, rectum (anus), under the arm, or inside the ear.
- feeling cold when nobody else does
- lack of appetite
- dehydration — preventable if the person drinks plenty of fluids
- hyperalgesia, or increased sensitivity to pain
- problems concentrating
If the fever is high, there may also be extreme irritability, confusion, delirium, and seizures.
Non-steroidal anti-inflammatory drugs (NSAIDs) such as Tylenol (paracetamol) or ibuprofen can help bring a fever down. These are available to purchase over-the-counter or online. However, a mild fever may be helping combat the bacterium or virus that is causing the infection. It may not be ideal to bring it down.
If the fever has been caused by a bacterial infection, the doctor may prescribe an antibiotic.
If a fever has been caused by a cold, which is caused by a viral infection, NSAIDs may be used to relieve uncomfortable symptoms. Antibiotics have no effect against viruses and will not be prescribed by your doctor for a viral infection.
Fluid intake: Anyone with a fever should consume plenty of fluids to prevent dehydration. Dehydration will complicate any illness.
Heat stroke: NSAIDs will not be effective if the person’s fever was caused by hot weather or sustained strenuous exercise. The patient needs to be cooled. If they are confused or unconscious, they should be treated by a doctor straight away.
Fever can be caused by a number of factors:
- an infection, such as strep throat, flu, chickenpox, or pneumonia
- rheumatoid arthritis
- some medications
- overexposure of skin to sunlight, or sunburn
- heat stroke, resulting either by exposure to high temperatures or prolonged strenuous exercise
- silicosis, a type of lung disease caused by long-term exposure to silica dust
- amphetamine abuse
- alcohol withdrawal
Fevers can be classified according to how long they last, whether or not they come and go, and how high they are.
A fever can be:
- low grade, from 100.5–102.1°F or 38.1–39°C
- moderate, from 102.2–104.0°F or 39.1–40°C
- high, from 104.1–106.0°F to or 40.1-41.1°C
- hyperpyrexia, above 106.0°F or 41.1°C
The height of the temperature may help indicate what type of problem is causing it.
Length of time
A fever can be:
- acute if it lasts less than 7 days
- sub-acute, if it lasts up to 14 days
- chronic or persistent, if it persists for over 14 days
Fevers that exist for days or weeks with no explanation are called fevers of undetermined origin (FUO).
Children with a high temperature may develop a febrile seizure, also known as a febrile fit or febrile convulsion; most of these are not serious and can be the result of an ear infection, gastroenteritis, or a respiratory virus, or a cold. Less commonly, febrile seizures may be caused by something more serious, such 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.
Seizures occur 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 might urinate, defecate, or both. There could 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 than simple febrile seizures.
In most cases, a child with a seizure should be seen by a healthcare provider. Temperature may be controlled with acetaminophen (paracetamol) or sponging. If necessary, an anticonvulsant, such as sodium valproate or clonazepam may be prescribed.
Diagnosing a fever is straightforward – the patient’s temperature is taken, if the reading is high, they have a fever. It is important to take the person’s temperature when they are at rest because physical activity can warm us up.
A person is said to have a fever if:
- The temperature in the mouth is over 37.7° Centigrade (99.9° Fahrenheit).
- The temperature in the rectum (anus) is over 37.5–38.3° Centigrade (100–101 Fahrenheit).
- The temperature under the arm or inside the ear is over 37.2 Centigrade (99 Fahrenheit).
Because fever is a sign rather than a disease, when the doctor has confirmed there is an elevated body temperature, certain diagnostic tests may be ordered. Depending on what other signs and symptoms exist, these may include blood tests, urine tests, X-rays, or other imaging scans.
Hygiene — fevers are commonly caused by bacterial or viral infections. Good hygiene practices help reduce the risk of developing an infection. This includes hand-washing before and after meals, and after going to the toilet.
A person with a fever caused by an infection should have as little contact as possible with other people, to prevent the infection from spreading. Whoever is caring for the patient should regularly wash their hands with warm soap and water.