Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 15, 2015

Fever is not an illness in itself, but can be the first sign of many illnesses. The underlying cause is usually a bacterial or viral infection. The seriousness of a fever depends on its temperature, duration and the age of the person. These factors also help to determine how the symptom should be managed and how the underlying illness should be treated.


Definition & Facts

A fever is a body temperature that is above what is considered normal. Though people tend to use 98.8 degrees Fahrenheit (37,1 °C) as the starting point for a normal thermometer reading, the average person's normal temperature range is between 91.8 and 100.8 degrees Fahrenheit (or 33,2-38,2 °C) and depends on where and when it is taken. While any elevation above normal temperature can cause concern, especially in new parents, it is not usually necessary to seek medical attention for a fever under 100.4 degrees.

A person's temperature can be taken orally, rectally or under the armpits. Temperatures taken rectally can vary by about 1 degree from temperatures taken orally. For infants, rectal temperatures are considered the most accurate. A person can also take a tympanic reading - that is, use a thermometer that is inserted in the ear. However, these thermometers are not accurate for measuring temperature in a child under three years old.

Because fever is the body's way of resisting attacks from germs, some practioners recommend not treating a fever that is low or that does not cause additional discomfort. Letting these fevers run their course can help to shorten the length of the underlying illness as well as boost immunity to future illnesses.


Although bacterial and viral infections are the most likely causes of fever, an elevated temperature can be caused by any foreign toxin that enters the body. The immune system treats fungi, certain drugs, mold and other substances as invaders. Raising the body's temperature is how the body attempts to fight these intruders.

Low grade fevers following shots or while teething are common in children and are no reason for concern. Other causes of fever in both adults and children include reactions to certain medicines, autoimmune diseases and even cancer.

There are other conditions that are sometimes confused for fevers because they are categorized by a heightened body temperature. Hyperthermia is one such condition, but unlike a fever, it is usually caused by external conditions such as exposure to excessive heat or wearing too much clothing. Hot flashes are also sometimes mistaken for fever, but these temperature changes are due to hormonal fluctuations.

When to see a doctor

A baby under 4 months old with a temperature over 100.4 degrees Fahrenheit (38 °C) should be taken to the hospital. Any child with a temperature over 104 F (40 °C) should also see a doctor as this can lead to serious complications, including febrile seizures.

Children and adults with fevers who also have sore throats, rash, headache and stiff necks should see a doctor immediately. These can be signs of a serious illness such as strep throat.

Adults and children with fevers that are greater than 104 F and accompanied by other symptoms such as hallucinations and convulsions should also get to a hospital. If a fever in a child lasts more than three days or more than a week for an adult, seek medical attention.

Fevers can sometimes be signs of a life-threatening illness such as meningitis or pneumonia. In the elderly or people with compromised immune systems. fevers should be given immediate attention to prevent complications.

Treatment & Therapy

Most fevers do not require treatment, but the discomfort they cause can prompt the desire for some kind of relief. Acetaminophen, ibuprofen and naproxen are the most common nonprescription treatments for pain and fevers due to illness. If a fever is caused by a bacteria, then antibiotics may also be prescribed. Viral infections, however, have to be waited out as antibiotics will not help.

For infants with a low grade fever that is not related to any other illness, a cool bath may be helpful. Taking off heavy clothing can ensure that the baby is as comfortable as possible. If the baby is fussy or refusing to eat, these things should be noted when speaking with the doctor.

Anyone with a fever would benefit from keeping hydrated by increasing fluid intake. Cool fluids like juices and water as well as hot herbal tea and soup can be soothing. However, caffeinated beverages and alcohol should be avoided as they can contribute to dehydration. It is also important to get plenty of rest.

While adults may take occasionally take aspirin to deal with a fever, children and teens should not take this drug as it has been linked to an increased risk of developing Reye's syndrome. This condition can cause damage to the brain and liver.

Prevention & Prophylaxis

Preventing fevers means preventing the illnesses that can lead to them. This is especially important in winter months, when cold and flu viruses can be spread. Proper hand washing is the most crucial measure to prevent the spread of sickness. A person should avoid touching his or her face and mouth as much as possible.

It is also important to keep things clean at home and at work. Wipe down hard surfaces with bleach solution or soap and water. Spraying surfaces with disinfectant also helps to prevent the spread of germs.

Avoiding sick people can also help prevent the spread of illnesses that cause fevers. Those who are sick and have fevers should be kept in one room so that others in the house are not needlessly exposed to their germs. Caretakers should make sure to wash their hands and any other surfaces that come into contact with those who are sick.

When there is a viral or bacterial infection that is going around, avoid sharing utensils, cups and clothing. A person may spread an illness before becoming symptomatic, so simply avoiding sharing these items with someone who is known to be sick will not help.

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