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Fever: What it is and When to Worry


We all worry about our kids when they are sick. And high fevers are scary. But there is a lot of misinformation out there on what a fever is and when we need to worry. Stay tuned for what is (and isn’t!) a fever and when you need to worry.

What is a Fever

Fever is a body temperature of over 100.4 degrees Farenheit (38 degrees Celsius). This is true for everyone. Body temperatures vary throughout the course of the day. Sometimes they are higher and sometimes they are lower. Some folks run normally at 97.0.  Others run lower.  Some run at 99 degrees. Regardless of what your “normal” is, a fever is STILL considered 100.4 and above.

How should you take your child’s temperature?

The most accurate way to tell if your baby or child has a fever is with a rectal or oral temperature reading. Unfortunately, temporal, ear, and under arm readings are often inaccurate.


In babies, the only way to accurately check for fever is with a rectal thermometer. Many rectal thermometers read very quickly and are marked to let you know how far to place the thermometer. This will not hurt your baby. And once you get over your unease, it will not hurt you either. Unfortunately, temporal, ear, and under arm readings are often inaccurate. If you are nervous about checking your baby’s temperature via rectal thermometer, check out How to Take a Child’s Temperature put out by A rectal temperature over 100.4 is a fever.

Older kids

After 3 years old, many kids do well with an oral thermometer. Make sure you use a different thermometer than the one you used for rectal temps.  Label them if necessary. Digital thermometers read very quickly and you can get a good read in under a minute.  The thermometer sits under your child’s tongue. An oral temperature over 1o0.4 is a fever.

What about axillary (under the arm) temps? Many schools use axillary temps to screen students who are feeling bad. We used to routinely add a degree to underarm temps. But now we do not. When your doctor asks about fevers, just tell them the number your thermometer registered and then tell them how you took it. An axillary temperature over 100.4 is a fever.

Temporal thermometers are another option for taking your kid’s temperature. These are quick and easy to use. And they can be great screening tools for kids down to 3 months of age. But if you keep getting a different number on it, or they seem much hotter than it is reading, try a rectal or oral temperature instead. A temporal thermometer reading over 100.4 is a fever.

What if my newborn has a fever?

If your baby is under a month old and has a fever of 100.4 or higher, they need to be seen. If this happens while the clinic is open, call your pediatrician and get in. After hours, call the doctor’s after hours line.  Newborns with fevers MUST be evaluated urgently. Do not give Tylenol, get them seen. If you can’t get in with your doctor, go to the emergency room. Newborns can get very sick very fast and with very few other signs of illness.

What if my infant or toddler has a fever?

Babies get sick sometimes.  If your infant (under 3 months) has just had immunizations and has a fever, it is generally safe to treat the fever and keep an eye on them. But if they are acting sick and have an unexplained fever, get them checked out. Your doctor will have a lower threshold for worry in a young infant with fever.

If your baby is between 3 months and 3 years and feels warm or is acting ill, it is reasonable to check their temperature. As above, over 100.4 is a fever. But not all fever is reason to worry. If your 2-year-old has a fever of 102 and is leaping over the furniture, they are ok. It is totally fine to keep an eye on them at home for a few days and see how things play out. The most common cause of fevers in our kiddos is a virus. And there are LOTs of different viruses.

Fever in and of itself is not dangerous. It IS a sign that our bodies are fighting off something. It is a good rule of thumb to treat the kid and not the fever. So if your kid has a fever and is perfectly normal, leave them alone. And if your kid has a fever and is really not acting well, has a rash, or other concerning symptoms, or is not improving with Tylenol or ibuprofen, get them checked out.

What if my infant or toddler’s temperature is REALLY high?

If your child has a high temp (>104) or at any point with a lower temp is really not acting like themselves, they need to be seen. Most kids who are acting fine between doses of fever reducer do NOT need to go to the emergency room. If you think your child needs to go to the ER, call your doctor to discuss. Most pediatricians try to keep kids out of the ER if at all possible. The ER is designed to take care of emergencies. And although a fever may feel like an emergency, in most cases, it is not. So you may be waiting a while.

What if my school-aged kid has a fever?

School-aged kids get sick. They touch everything and are very hands-on in all they do. (mostly, they are gross… at least, mine are!) Many times, it is completely fine to keep an eye on them for a few days. However, for severe symptoms or fevers that last longer than 5 days, it is best to get your kiddo checked out.

Concluding thoughts

Fevers are no fun. But they are a common part of routine childhood illnesses. So knowing when to worry is important. Nearly always, it is how your little one is acting that is the most important factor in an illness.

1. Fever 100.4 or higher in a baby under a month is an emergency. They need to be checked out ASAP.

2. Most fevers are more bothersome than a cause for concern. But if your kid is not acting right, they need to be seen.

3. Kids who have persistent fevers (>5 days) need to be seen.

4. Fever is 100.4 or higher.

5. Kids with fever > 104 need to get checked out.

I do hope that this has cleared up some confusion about fevers. Stay tuned for a coming post on viruses. Gotta love cold and flu season!

Posted in Common childhood illness, General, Infants and Toddlers, Middle and High School, Parenting, Preschool and elementary, Safety

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