What temperature is a fever? Is high fever dangerous for a baby?

Infectious Diseases

What temperature is considered a fever?

Understanding what your child’s temperature means is essential and can be a quick way of telling if they are sick.

When assessing your child’s illness, many doctors will ask if your child has had a fever, how high it has gotten, and how many days it has lasted. Being able to identify a fever in your child should be part of your parental first aid kit. It’s a significant first step in deciding if your child needs to be seen by a doctor.

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What is a Normal Body Temperature?

Determining normal body temperature depends on where you are taking the temperature so you can determine if your child has a high fever or a low-grade fever.

The below table is a great guide for normal body temperature taken at different parts of the body. You can use a digital thermometer or manual thermometer.


Location Celsius (oC) Fahrenheit (oF)
Rectum 36.6 – 37.9 97.9 – 100.3
Mouth 35.5 – 37.9 95.9 – 100.3
Armpit 34.7 – 37.3 94.5 – 99.1
Ear 35.8 – 37.9 96.4 – 100.4


*Note: This guide is not just for babies and can be used as a normal temperature guide for children and adults. Ear temperature readings can be inaccurate between each ear. Armpit temperature readings are more accurate in older children than ear measurements.

What is considered a low-grade fever?

You can see here that if your measurement is rectal or oral, a low-grade fever is considered around 38 degrees Celcius or 100.4 degrees Fahrenheit. Again, this can be taken with a manual or digital thermometer.


What temperature is considered a fever?

Same answer as above! A fever starts at 38 degrees Celcius or 100.4 degrees Fahrenheit if measured in the mouth or rectum. So, where fever starts is the same as a low-grade fever.

A rectal thermometer is the best method to measure body temperature in children less than two years of age. But few parents are comfortable with performing rectal temperature readings. Mouth temperatures are the second most accurate, followed by armpit or axillary temperatures.

Ear thermometers are routinely inaccurate (frequently, there is a discrepancy in temperate between the two ears). The inaccuracy is seen most prominently with ear infections, as the infected ear is often warmer.

Another popular thermometer that parents use is an infrared thermometer since it’s less invasive and can read body temperature without physical touch.

When in doubt, see your doctor for an accurate temperature reading.


Your child’s behavior and how they are acting are also important. Pay attention to signs like fatigue, panting, and confusion. If a child has a fever, but they are feeling well, not complaining, and they are drinking well and interacting, as usual, there is no need to rush to lower it. How your child LOOKS is far more important than the number on the thermometer.


What body temperature is considered a fever?

Anything above the normal range by ~0.5o Celsius is considered a fever. A fever can seem scary, but it’s a natural response that helps the body fight infections.

As a general rule of thumb, you should see a doctor for children less than six months old if your child has a fever.

Babies less than two months of age cannot fight infections as easily, and fever in this age group may signal a bacterial infection that requires medication to treat.

If you have a baby who is less than two months of age and has a fever, please go to your nearest emergency room. DO NOT give fever-reducing medication. Instead, go to the emergency room, as the nurses and doctors will want to take the temperature themselves there first.

Read more about how to reduce a fever and safely maintain a normal body temperature for your child.

If you have a child younger than two months with a fever, please seek medical attention ASAP.

A fever will typically last for 72 hours or less for children above two years of age and can be treated at home. However, after 48-72 hours of fever, I suggest seeing your doctor to rule out any treatable infections.

Babies less than two months of age cannot fight infections as easily, and fever in this age group may signal a bacterial infection.


Quick Tips on Babies, Kids, and Fever:

• Normal body temperature is about 37oC or 98.6oF

• A fever is anything above 38 oC or 100.4 oF. Read more about the causes of a fever and when it’s serious.

• Fever is not the whole story – pay attention to your child’s behavior!

• Only treat a fever in your child when it’s causing discomfort.

• For febrile children < 2 months – see your doctor immediately.


FAQs – Frequently Asked Questions


Is a rectal temperature as accurate as other thermometers?

Rectal temperatures are the most accurate for checking a child’s temperature. Therefore, it is best to measure body temperate in an infant less than two rectally. However, an oral and ear digital thermometer can measure body temperature and be used for older children.


Is it normal for babies to have body heat?

Average normal temperature for infants aged 0–2 years ranges from body temperatures between 97.4–100°F when taken rectally.


Does serious infection raise body temperature?

When you’re sick, their temperature may go up or down. A normal temperature is 97.4 -100°F. Low body temperature is below 97.4°F.


What are other symptoms of fever?

A fever is a peak in body temperature, which can be caused by an infection. You may be feeling sick because of your higher than normal core temperature, and other signs include sweating, chills, or shivering with muscle aches. Other symptoms include loss of appetite or irritability, cough, congestion, vomiting, or diarrhea from the illness causing the fever.


Does fever cause a stiff neck?

A stiff neck is not always serious but could result from a very bacterial infection or other serious infection. If your child has a stiff neck, please see a healthcare provider immediately, or go to your nearest emergency room for a physical examination and evaluation.

Dr Dina Kulik - Kids Health

Dr. Dina Kulik, MD, FRCPC, PEM

Written By: Dr. Dina Kulik, MD, FRCPC, PEM

Dina is a wife, mother of 4, and adrenaline junky. She loves to share children’s health information from her professional and personal experience. More About Dr Dina.

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