Health Stories

Everything You Ever Wanted to Know about Fever

When it comes time to fever in children, we worry about doing the right thing; knowing when to act and when to let nature takes its course. The Children's Hospital of Eastern Ontario (CHEO) sees a lot of concerned parents in our Emergency Department with children who may or may not need medical intervention. To help demystify fever, CHEO recently put together a fever guide to answer your questions about what to do when your child has a fever. Here we offer you an overview of the fever guide's information.

What is a fever?

Fever is the body's normal way of fighting infection. Fever lets us know that something is going on — it's a flag for us to keep an extra watch on how a child is acting.

The best way to take the temperature of a child under 3 years is rectally. Using a digital thermometer is quickest and safest. If using a glass thermometer, it must be shaken to below the first number before use and held in place for at least 5 minutes.

You know your child has a fever if the temperature is greater than:

  • 38.5°C or 101.3°F rectally.
    To take a rectal temperature, place the tip of the lubricated thermometer 1-2 cm (½ to ¾ inch) in rectum.
  • 38.0°C or 100.4°F by mouth.
    Take a temperature by mouth only if your child is older than 3 years and can keep the thermometer under his or her tongue.
  • 37.5°C or 99.5°F underarm.

When you use the underarm to measure temperature, make sure the tip of the thermometer is in the centre of the armpit.

CHEO does not recommend that you take your child's temperature with an ear (tympanic) thermometer, electronic pacifier, or forehead strip, as they are not accurate.

Putting the fever in perspective

  • A LOW GRADE FEVER is a rectal reading between 38°C (100.4°F) and 39°C (102°F). This is the normal body reaction to fighting infection.
  • A MODERATE GRADE FEVER is a rectal reading between 39°C (102°F) and 40°C (104°F). If their temperature is in this range, you should give your child medication to bring the temperature down to low grade.
  • A HIGH FEVER is a rectal reading over 41°C (106°F). At this point, you should give your child medication to bring down the fever and see your doctor. Fevers are only harmful if they are above 42.3°C (108°F)
  • Children under 2 months with a rectal temperature over 38°C (100.4°F) should see a doctor.

How your child looks and acts is more important than the number on the thermometer.

What to do?

  • If you think your child has a fever, dress him or her lightly and take the temperature again in 30 minutes, to make sure it is a fever.
  • Encourage your child to drink fluids. Children lose a lot of water when they have a fever.
  • Dress your child in one layer of clothing and avoid bundling your baby with blankets.
  • Sponge, alcohol and cool baths are not recommended and may make your child more uncomfortable.
  • Many children get a fever after immunizations — give medication to lower the fever if needed.
  • Medication for a fever can include acetaminophen (like Tylenol and Tempra) or ibuprofen (like Advil or Motrin). It is important to give medication according to your child's weight and not only according to age. Call your pharmacist, doctor or one of the information lines listed below if you need help.
  • Fever medication will bring temperature down 1-2 degrees, and last 3-4 hours.
  • If your child still has a fever and is not comfortable after 4 hours, you can repeat acetaminophen.

In general, when your child has a fever, he or she can be safely cared for at home.

Contact your doctor if your child is:

  • Very irritable (cries when touched or moved);
  • Developing a rash;
  • Not eating or drinking;
  • Looking and acting very sick; or
  • Feverish for longer than 3 days (72 hours).

Go to the hospital if your child is:

  • Having difficulty breathing;
  • Unable to swallow;
  • Confused;
  • Very sleepy and hard to wake up; or
  • Has not wet a diaper in more than 8 hours.

Parents are often concerned that a child's fever will cause a seizure. It is important to note that the risk of seizures is very low. In addition, seizures from fever are not known to cause any long-term problems.

This information about fever may not be suitable for children with chronic illnesses or children under two months. In these cases, contact your doctor.

If you have any questions call your doctor, or the Ottawa Public Health Information Line 613-580-6744 ext. 28020.

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