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What to know about a fever and kids 🤒

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Fever is anything over 100.4 degrees Fahrenheit or 38 degrees Celsius.

Check out the PedsDocTalk YouTube Video: Fevers in Children, Babies and Kids — When to Worry? For more details on why kids get fevers, thermometers, how to check a rectal temperature, when to treat a fever, common fever myths, and when to seek care.

Fever is the number one reason we get phone calls in the middle of the night as general pediatricians. And it’s also the number one reason you may go to the ER or come to our offices. Many times fever is not a cause for concern.

I have many parents come in and say “hey, doc, my child has a 99.8 fever.” 99.8 is a higher temperature, but it’s not considered a fever. 100.3 is not considered a fever, either and we have to put the number somewhere. And so we set it at 100.4 Fahrenheit or 38 degrees Celsius.

Fever is the body’s natural response to fighting something that they don’t like and viruses are largely the reason kids develop fever. Fever causes a whole plethora of inflammatory agents that help fight an illness. So in some ways, fever is good. Read on for when to get a fever evaluated.

What thermometer to use?

Try not to stress so much about the brand. I like a thermometer that has options for axillary (underarm), under the tongue (oral), and rectal. These thermometers can be purchases with covers for each use.

If you don’t want to use a rectal reading, because your child’s a toddler, that is fine. You can do under the arm or in the mouth. But we do absolutely recommend if your child is under three months of age that you stick to a rectal reading – I’ve had many times where parents will check a forehead temperature reading on their two-month-old or an ear thermometer reading on their two-month-old and it’s falsely high or falsely low.

So just go directly for the rectal temp, apply a little bit of that Vaseline and insert it into the rectum for the most accurate reading.

If your child is under two months of age and has a temperature over 100.4, (which is a fever), you need to see your pediatrician, call them or go to the ER.

Under 1 month of age, they need to be seen immediately in a hospital. If they are between one month to two months and have a fever, speak to your child’s clinician or their staff. Your baby will likely need to be evaluated in the office or a hospital, depending on their symptoms.

Fever is something we need to evaluate in a baby under two months because their immune systems are more delicate and they don’t have a developed blood-brain barrier that basically keeps things separate from the blood and separate from the brain. So we want to make sure that there’s no infection that’s coming into the blood or brain. If your baby under one month has a confirmed fever, they may need bloodwork, a urine sample, and a LP (procedure that takes fluid from the spinal cord) to make sure there is no concern for a bacterial infection. If they are showing any signs of congestion or cough, they may also need a viral swab to confirm if the cause is able to be a documented virus.

If your child is over one month, they may do a limited workup that begins with a urine study and bloodwork and depending on that and how the baby looks, may proceed to an LP.

Between two months to three months with a fever, speak to your child’s clinician or their staff. They will want to know what symptoms your baby has, any sick contacts, how they are feeding, and how many wet diapers they are making. If they’re doing well, they will ask you to come in at the next available appointment or give you some things to monitor.

Three main things to look out for.

There are three main things I want you to look out for when your child has a fever.

  1. Is your child making wet diapers or urinating?
  2. Is your child breathing comfortably
  3. Is your child having any difficulty being consoled and age-appropriate medications like Ibuprofen (for over 6 months) or acetaminophen (over 2 months) are not working?

If any of those three things are happening, you can talk to your pediatrician.

Watch this PedsDocTalk YouTube Video for more information on when to treat a child with a fever and when to seek care for a fever.

Your gut is important as a parent or caregiver.

So if you are concerned and your child is not acting well, we are here for you. Make sure you understand when to be concerned and make sure you understand that you do not need to over-medicate your child, focus more on how they’re acting. Understand the best way to check a temperature, which is again, rectal under three, and then also understand when to seek medical care.

Remember, fever is common after the two-month vaccines, but NOT the Hepatitis B given at birth or at one month.

If your baby has a fever after the two-month vaccines, this can be monitored as long as they are consolable and hydrated. If the fever persists post-vaccine for more than three days, it’s a good idea to get them evaluated.

Do you know WHEN to treat fever? It comes down to their comfort. Symptoms are way more important than the number on the thermometer.

Watch the PedsDocTalk YouTube Video: Fever in children, babies, and kids – When to Worry?


Dr. Mona Admin

Hi there!

I’m a Board Certified Pediatrician, IBCLC, and a mom of two.

I know the ups and downs of becoming a mom and raising kids.

I help moms ditch the worry and second-guessing so you can find more joy in motherhood.


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All information presented on this blog, my Instagram, and my podcast is for educational purposes and should not be taken as personal medical advice. These platforms are to educate and should not replace the medical judgment of a licensed healthcare provider who is evaluating a patient.

It is the responsibility of the guardian to seek appropriate medical attention when they are concerned about their child.

All opinions are my own and do not reflect the opinions of my employer or hospitals I may be affiliated with.