Oral temperature
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An oral temperature of 37.8°C (100°F) or higher means a fever.
A fever can be a sign that the body is fighting an infection. When the body's defense (immune) system is activated by a germ, many reactions occur in the body. Fever is one sign of these reactions. Fever is not a disease or illness itself.

Measuring body temperature

Children often feel warm to the touch when they have a fever. To confirm that your child has a fever, use a thermometer to measure your child's body temperature.

  • In a baby, the most accurate way to measure temperature is with a thermometer inserted into the anus (rectal temperature). A rectal temperature of 38°C (100.4°F) or higher means a fever.
  • In older children, the temperature can be measured by mouth (oral temperature). An oral temperature of 37.8°C (100°F) or higher means a fever.
Rectal temperature
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A rectal temperature of 38°C (100.4°F) or higher means a fever.

Other methods of measuring temperature may sometimes be useful, but the measurement may be less accurate. These methods include:

  • using a thermometer in the armpit (axillary temperature); a temperature of 37.2°C (99°F) or higher means a fever.
  • using an ear thermometer (tympanic temperature); a temperature of 37.5°C (99.5°F) or higher means a fever.

What causes fever?

Many different infections can cause a fever. To find out what is causing your child's fever, the doctor will look at other signs or symptoms of the illness, not the fever itself. How high a fever is does not help the doctor to decide whether an infection is mild or severe, or whether an infection is from a bacterial or viral illness. It is important to know how many days of fever your child has had. You should keep a record of your child's fevers so that you can accurately tell the doctor how long the fever has been present.

Armpit temperature
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An armpit temperature of 37.2°C (99°F) or higher means a fever.

Fever may also be caused by other conditions:

  • A mild increase in body temperature can occur with exercise or too much clothing, after a hot bath or shower, or in hot weather.
  • Rarely, heat stroke or exposure to certain medicines or drugs can cause a severe and possibly dangerous increase in body temperature.
  • Vaccinations can cause fever.
  • Some non-infectious illnesses and inflammatory conditions can cause recurrent or persistent fevers.

Many people believe that teething causes fever. Research shows us that teething does not cause real fever. If your baby has a fever, do not assume it could be due to teething It is important to see your child's doctor.

What to expect when your child has a fever

Fevers can make children feel uncomfortable. Usually, these symptoms are mild and the child may be slightly cranky or have aches and pains. Some children are less active and more sleepy. Some fevers may be associated with shaking (chills or rigors) as the body temperature is changing. This type of shaking is one way for the body to try to regulate the temperature. It is not a seizure or convulsion, and is not associated with changes in the child's level of consciousness.

Ear temperature
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An ear temperature of 37.5°C (99.5°F) or higher means a fever.

Approximately 5% of children between the ages of 6 months and 6 years may have a shaking episode called a seizure or convulsion associated with a fever. These are called febrile seizures. Your child should see a doctor after a febrile seizure, but febrile seizures are generally not dangerous.

How often the fever recurs and how long the fever lasts depend mostly on the type of infection causing the fever. Most fevers with viruses last for 2 to 3 days, but sometimes they can last as long as 2 weeks. When the fever is caused by a bacterial infection, it may continue until the child is treated with an antibiotic medicine.

Taking care of your child with a fever


Keep your child lightly dressed. Most body heat is lost through the skin, so overdressing or bundling your child may result in a higher fever and can make your child more uncomfortable. If your child is having chills or shivers, give her a light blanket. Keep the room temperature at a level that is comfortable for you, when lightly dressed.

Extra fluids

Fever will make your child's body lose slightly more fluid (liquid), so encourage your child to drink extra fluids. Cool water or drinks may be helpful, but it does not really matter whether the drinks are warm or cool.


Sponging is not necessary to help lower body temperature, and may make your child more uncomfortable. Sponging may just cool the outside of your child's body and cause her to shiver, without really affecting the internal body temperature. Use sponging only in an emergency such as heat stroke.


Medicine can help to reduce the fever. Medicines may only reduce the fever by 1°C to 2°C (2°F to 3°F), and may not bring the temperature down to normal. Fevers may also cycle up and down on their own, so it is not always easy to tell whether a fever is reduced because of medicine or because of the natural fever pattern. If your child is sleeping comfortably, it is not necessary to wake her up to give these medicines.

Two types of medicines are usually recommended for managing fever. They are:

  • acetaminophen (Tylenol®, Tempra, Abenol®, drug store and other brands)
  • ibuprofen (Advil®, Motrin®, Brufen, drug store and other brands)

They are both available in tablets, capsules, and liquid formulations of various strengths. Acetaminophen is also available as a rectal suppository. This is a good method of delivery for babies since you put the medicine directly into their rectum (bum). Only a rectal suppository can be used this way. Do not put a tablet intended for the mouth into a child's rectum.

Your doctor or pharmacist can help you decide on the most appropriate formulation and strength for your child. The correct dose for a child is based on body weight. An estimated dose is usually provided on the medicine package.

These medicines are used to help manage the fever and to make your child more comfortable, but they do not treat the underlying cause of the fever.

If your baby is less than 3 months old and has a fever, you need to see a doctor immediately. Fever in a newborn may be a sign of a serious infection. If this happens on the weekend, do not wait to see your doctor. Go to the nearest Emergency Department to have your baby assessed right away by a doctor. Do not give any fever medicines to your baby unless a doctor says so.

Acetaminophen and ibuprofen do not interact with each other. They may be equally effective in lowering a temperature.

If your child has a pre-existing medical condition or is already taking other medicines, talk to your child's doctor to make sure that acetaminophen or ibuprofen is safe for your child.

Do not use ASA (Aspirin) to treat your child's fever

Although rare, ASA (acetylsalicylic acid or Aspirin) has been linked to a severe condition called Reye's syndrome. Do not give ASA to a child to manage a fever unless your doctor has specifically told you to give it. You may need to check the label of other medicines or ask your pharmacist to make sure that they do not contain ASA.

When to see a doctor

See your child's regular doctor or go to the nearest Emergency Department right away if your child has a fever and:

  • your child is less than 3 months old
  • you have recently returned from travelling abroad
  • your child develops a rash that looks like small purple dots that do not go away when you apply pressure with your fingers (blanching)
  • your child is not able to keep down any fluids and appears dehydrated
  • your child's skin looks very pale or grey, or is cool or mottled
  • your child is having constant pain
  • your child is lethargic (very weak) or difficult to wake up
  • your child has a stiff neck
  • your child has a seizure associated with fever
  • your child is looking or acting very sick
  • your child seems confused or delirious
  • your child does not use his arm or leg normally or refuses to stand up
  • your child has problems breathing
  • your child cries constantly and cannot be settled

See a doctor within 24 hours if your child has a fever and:

  • your child is between 3 and 6 months old
  • your child has specific pain, such as ear or throat pain that may require evaluation
  • your child has had a fever for more than 3 days
  • the fever went away for over 24 hours and then came back
  • your child has a bacterial infection that is being treated with an antibiotic, but the fever is not going away after 2 to 3 days of starting the antibiotic
  • your child cries when going to the bathroom
  • your child's urine smells bad
  • you have other concerns or questions

Fever: Myths and facts

There are many myths about fever, and some of these myths may make you worry unnecessarily. If your child has a fever, the most important thing is how your child looks and acts.

Myth: The exact number of the temperature is useful

That is not true! The most important part of assessing a child with fever is how the child looks and acts, especially after treating the fever with medicine. A child who appears well but has a high temperature, for example, is less concerning than a child who only has a mild fever, but who appears quite unwell or is not responsive. Some minor viral illnesses may have high fevers associated with them, and some serious bacterial infections may be associated with an abnormally low body temperature.

Myth: Fevers cause brain damage

That is not true! Most fevers associated with infections are less than 42°C (108°F). These fevers do not cause brain damage. Only a persistent body temperatures greater than 44°C (110°F) can cause brain damage. These body temperatures are more likely to occur with heat stroke or after exposure to certain street drugs or medicines, such as anaesthetic or some psychiatric medicines. They do not occur with the usual infections that children can have.

Myth: Fevers are bad for children

That is not true! A fever is just a sign that the body's defense system has been activated. Fevers help to fight infections because many germs do not survive as well at slightly higher body temperatures. In this sense, although the child may be uncomfortable, most fevers have a beneficial effect and may help the body fight infection. The main reason to use medicine to decrease fever is to make the child feel better.

Myth: Fevers should always respond to an anti-fever medicine

That is not true! Anti-fever medicine usually helps to bring the fever down, but this is not always so. Sometimes a fever continues even after giving the medicine.

Myth: Fevers should respond quickly to antibiotic medicine

That is not true! Antibiotics are only useful in treating bacterial infections. They have no effect on viral infections. Most infections in children are caused by viruses, so an antibiotic will have no effect on them. For bacterial infections, the antibiotic will start working to fight the bacteria as soon as it is given, but it may take 2-3 days before the fever goes away.

Key points

  • If your baby is 3 months of age or younger and has a fever, see your doctor immediately.
  • Fever is usually a sign that the body is fighting an infection.
  • Pay attention to how your child looks and acts. Keep a record of the number of days of fever.
  • To keep your child comfortable, do not dress your child too warmly. Give your child lots of fluids to drink, and give acetaminophen or ibuprofen if it seems to make your child& feel better.

Elly Berger, BA, MD, FRCPC, FAAP, MHPE​​​​