Fevers: How High is Too High?

Despite having fever information on our website and blogging about it many times, including here and here and here, parents often call in or bring their child in with excessive concern for fevers. (Note: paracetamol is the same as acetaminophen and Tylenol in the linked article.)

The information here is only for infants and children over 3 months who are otherwise healthy and vaccinated. If those criteria are not met, the child is in a higher risk category.

Fever is one of the biggest anxiety inducers in parents, and I want that to change. Yes, we should care for our children when they're sick, but we don't need to worry about the numbers on the thermometer.

Maybe one time I'll explain fever in a way that hits home so parents can stop focusing on the number and more on the child. Parents often tell us in detail what the temperatures are at various points of the day but omit how the child looks and acts. I care more about the child's behaviors than the thermometer's reading.

I know fever is scary. Kids are miserable. But the temperature itself is not what we treat. Treat the symptoms!

What is a fever?

The number on the thermometer can be confusing to parents. How the temperature is taken is as important as the number itself to determine if it is a fever. A fever is often defined as a temperature over 100.4 °F (38 °C) but it can vary based on how you take the temperature (rectal vs oral vs forehead).

This is simply the minimum temperature that is no longer considered normal. The American Academy of Pediatrics doesn't recommend treating fevers until the temperature is over 102°F unless the child is uncomfortable. Thermometers are not very accurate, so when you worry more about a temperature that is 0.5 degree higher than another temperature, it might not even be a significant difference. You could take the temperature twice in a row and get different readings. If your child is playful and the thermometer reads 101.5°F that is a very different story than if your child is barely moving, whimpering, and breathing fast with a temperature of 101.5°F. I wouldn't recommend any fever reducers for the first, but I would recommend the second get evaluated by a pediatrician or other medical provider.

Why do we care about fevers?

I think medical professionals help to foster this fear of fevers because we ask about them. It can be helpful to know the actual temperature because many kids are warm but not really running a fever.

• We are more contagious during a fever, which is why schools and daycares won't let kids stay if they have a fever. 
• The height of the fever doesn't indicate if the child has an infection requiring antibiotics or not, but it can cause increasing discomfort as it rises above 102°F. 
• The height of a fever does not cause fever seizures, but a rapid change in temperature can cause a seizure in a child that is susceptible to them.
• If a true fever lasts more than 3-5 days or is accompanied by other concerning symptoms, the child should be seen to look for a source. 

So how high is too high?

Fevers higher than 106°F (41°C) might be the answer parents are asking when they want to know what temperature is too high. It is at this point that brain damage from the temperature itself can occur due to hyperpyrexia (heat stroke). This is not common from a simple infection and other symptoms will be present, such as change in consciousness, vomiting, flushed skin, headache, rapid breathing, and very rapid heart rate. Emergent medical attention and cooling the body is important with hyperpyrexia, which differs from fever.

If your child does not appear very ill and the thermometer reads very high, it is likely the thermometer is in error.

What if the temperature doesn't go down to normal after using a fever reducer?

When parents give a fever reducer, they often worry that the temperature doesn't go back to normal. Returning to normal doesn't mean it isn't a serious infection and not returning to normal doesn't mean that it is a serious infection. Studies show the temperature tends to decrease by 1.8 to 3.6°F. Acetaminophen begins to work in 30 - 60 minutes and has its peak effect in 3-4 hours. The duration of action is 4-6 hours. Ibuprofen begins to work in under 60 minutes and has its peak effect in 3-4 hours. The duration of action is 6-8 hours. The goal should be to make a child more comfortable though, not to get the temperature to normal.

My personal opinion is that most children won't need their temperature taken to verify that they are better. They should be more comfortable. If they aren't, then it is wise to have a medical professional look at them.

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If a child's temperature is usually low, how do we define fever?

My child typically runs a temperature around 97°F, so if the temperature is 99°F, is that a fever?

We get a variation of this question all the time.

Sometimes it's the opposite, such as my child usually runs hot, so can you write a note saying 101°F isn't a fever for him?

Short answer (both questions): No.

Long answer: Our body temperature is very complex. Your school district will define a fever with a number, but your doctor might have a different number. A fever is not defined by the change from a person's baseline temperature.

Disclaimer: All information on fever given is for healthy, vaccinated children over 3 months. Young infants, children with chronic disease, or undervaccinated kids do not apply to standard fever discussion and advice.

Most people think of a "normal" body temperature as an oral temperature of 98.6°F. Your temperature may normally be a degree or more higher or lower, which means 99.6°F is normal despite the fact that some daycares define this as a fever. Most often we associate high body temperatures with illness, but elevated temperatures also can be caused by environment temperatures being too high (or over bundled babies), dehydration, medications, poisons, cancer or overactivity. Your normal body temperature changes by as much as 1°F throughout the day, depending on how active you are and the time of day. Body temperature is very sensitive to hormone levels, so may vary with women’s monthly cycles. Our temperature tends to lower as we age - kids tend to have slightly higher temperatures than their parents, even when healthy. It is very common for children to get a fever when sick, but less common for adults. And the thermometer itself can vary in readings significantly, so the number may or may not be reliable, depending on the thermometer.

It is said that a child has a fever when his or her rectal temperature is 100.5°F or higher, which is about 99°F under the arm and 99.5°F and in the mouth. [This was edited 6/21/17 after some perceptive pediatricians found a typo.] This is by convention, but in actuality children’s normal temperatures may be higher than adults so these temperatures might be normal and only higher temperatures may actually indicate fever.

Parents often use the term "low grade fever" to indicate something less than 100.5°F. There is really no such thing. It's either a fever or it's not. A low fever in my mind means a temperature over 100.5°F that doesn't make the kid feel pathetic. Any temperature less than that simply isn't a fever. The child might be sick and temperature doesn't define illness, but it's not a fever.

There also isn't a medical definition of high fever. The temperature is the temperature and illness is better defined by describing all symptoms, not just the temperature. I guess if I had to define a high fever, it would be one that makes a person feel absolutely miserable. There is no magic number that defines this high fever or that tells us when to worry more. It's more important to look at the child than the thermometer to know if they're really sick or not.

Many parents have fever phobia, a condition where they worry that the fever itself will do damage. While a rapidly increasing temperature can cause fever seizures, these are more scary than dangerous. Fever seizures can occur with relatively low fevers if the change in temperature is rapid. It's not necessarily the high high temperatures that cause seizures. The brain will not be permanently damaged from most fevers (even high temperatures), though a fever can be a symptom of serious illness that can damage the brain, such as meningitis. But you would recognize that your child is more sick than the typical illness if they are having symptoms of such a significant illness. You would not use a thermometer to tell you that.

I do not recommend taking a child's temperature frequently. That causes excess worry in parents when the temperature increases by 0.5 degree, which could be a real change or just the thermometer's reading. Respond to your child, and don't rely on the thermometer. Never wake a comfortably sleeping child to take the temperature. Don't use sticky strip thermometers that tell your cell phone if there's a fever (yes, that exists, and it will lead to more parental anxiety than help keep children healthy.) Knowing the temperature helps to know if it is a true fever or not, but it should not direct you to give medicine or not. A temperature can be taken at times you need to know if there's a fever, since schools and daycares have rules to keep kids with fever away (though fever is not the only sign of illness and if your child's sick he might need to stay home despite temperature). It is sometimes helpful to know if a warm or hot child has a true fever, but you don't need to take it every hour to follow the trend with most illnesses. It's not even helpful to see how much medicine brings the temperature down. If a child doesn't improve, you will be concerned regardless of the thermometer reading. Taking a temperature once or twice a day is sufficient. I'd recommend taking it at times that it is likely to be its highest, such as in the evening or when fever reducing medicine has worn off.

The American Academy of Pediatrics recommends treating sick children for comfort, which is typically when the temperature reaches about 102°F or if they have pain somewhere. Not all earaches or sore throats cause fever, but you might consider a pain reliever to help symptoms. Most people feel uncomfortable as their temperature approaches 102°F. Only give fever reducers if the child needs it for comfort because the fever is actually helping the child fight off an infection - don't inhibit the immune system if your child is comfortable enough to sleep and drink without significant pain.

Never give a fever reducer to hide a fever so you can send your child to school or daycare. If they don't feel well, they shouldn't go because they'll spread the illness to other kids. A normal temperature because of a fever reducer does not mean that the child is fever free. You can only be fever free if the medicine has worn off and the temperature remains normal. The temperature should be normal off medicines for 24 hours before returning to school or daycare (or work for adults with fever).

So, with the original question, if a child is usually cooler than 98.6°F, when do they have a fever?

A temperature over 100.5°F is the general definition of fever, regardless of baseline temperature. In practical terms though, parents really want to know if a child is sick or not. You can tell when a child is uncomfortable by looking at him ~ you don't need a thermometer. It is not necessary to treat based on the thermometer reading. It is important to give a fever reducer/pain reliever when the child is uncomfortable so he can drink to stay hydrated and sleep. The goal is not to lower the temperature to “normal”, it's to make the child more comfortable.

If you are concerned about your child's illness, especially if he looks dehydrated, is having trouble breathing, is in uncontrollable pain, has symptoms you think might need antibiotics (such as UTI symptoms or Strep throat), or if the fever lasts more than 3-5 days (depending on age of child and overall symptoms), bring him to have an exam to look for sources of fever. 

Related blogs:

Fever is... 
Evolution of illness
But the snot is green
Adenovirus infections
To Tamiflu or Not to Tamiflu
Tamiflu: Guest blogger Dr. Mark Helm
Urgent cares for routine illness: Yes or No?
New Guidelines for treating Strep throat
Updated sinusitis guidelines
All about ears
Menthol for sore throats and cough
My child's cough sounds like...
Cough medicines: Which one's best?
How long with a cough or cold last?

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Fever is...

 

Fever is scary to parents.

Parents hear about fever seizures and are afraid the temperature will get so high that it will cause permanent brain damage.  In reality the way a child is acting is more important than the temperature.  If they are dehydrated, having difficulty breathing,  or are in extreme pain, you don't need a thermometer to know they are sick.

Fever is uncomfortable.

Fever can make the body ache. It is often associated with other pains, such as headache or earache.  Kids look miserable when they have a fever. They might appear more tired than normal.  They breathe faster. Their heart pounds. They whine.  Their face is flushed. They are sweaty.  They might have chills.

Fever is often feared as something bad.

Parents often fear the worst with a fever: Is it pneumonia? Leukemia? Ear infection?  

Fever is good in most cases. 

In most instances, fever in children is good.  It is a sign of a working immune system.  

Fever is often associated with decreased appetite.

This decreased food intake worries parents, but if the child is drinking enough to stay hydrated, they can survive a few days without food.  Kids typically increase their intake when feeling well again.  Don't force them to eat when sick, but do encourage fluids to maintain hydration. 

Fever is serious in infants under 3 months, immune compromised people, and in under immunized kids.

These kids do not have very effective immune systems and are more at risk from diseases their bodies can't fight.  Any abnormal temperature (both too high and too low) should be completely evaluated in these at risk children.   

Fever is inconvenient.

I hate to say it, but for many parents it is just not convenient for their kids to be sick.  A big meeting at work.  A child's class party.  A recital.  A big game or tournament.  Whatever it is, our lives are busy and we don't want to stop for illness.  Unfortunately, there is no treatment for fever that makes it become non-infectious immediately, so it is best to stay home.  Don't expose others by giving your child ibuprofen and hoping the school nurse won't call.

Fever is a normal response to illness in most cases.

Most fevers in kids are due to viruses and run their course in 3-5 days.  Parents usually want to know what temperature is too high, but that number is really unknown (probably above 106F). The height of a fever does not tell us how serious the infection is.  The higher the temperature, the more miserable a person feels.  That is why it is recommended to use a fever reducer after 102F.  The temperature does not need to come back to normal, it just needs to come down enough for comfort.

Fever is most common at night.

Unfortunately most illnesses are more severe at night.  This has to do with the complex system of hormones in our body. It means that kids who seem "okay" during the day have more discomfort over night.  This decreases everyone's sleep and is frustrating to parents, but is common.  

Fever is a time that illnesses are considered most contagious.

During a fever viral shedding is highest.  It is important to keep anyone with fever away from others as much as practical (in a home, confining kids to a bedroom can help).  Wash hands and surfaces that person touches often during any illness.  Continue these precautions until the child is fever free for 24 hours without fever reducers.  (Remember that temperatures fluctuate, so a few hours without fever doesn't prove that the infection is resolved.) 

Fever is an elevation of normal temperature.

Normal temperature varies throughout the day, and depends on the location the temperature was taken and the type of thermometer used.  Digital thermometers have replaced glass mercury thermometers due to safety concerns with mercury.  Ear thermometers are not accurate in young infants or those with wax in the ear canal.  Plastic strip thermometers and pacifier thermometers give a general idea of a temperature, but are not accurate.  

To identify a true fever, it is important to note the degree temperature as well as location taken.  (A kiss on the forehead can let most parents know if the child is warm or hot, but doesn't identify a true fever and therefore the need to isolate to prevent spreading illness.)  I never recommend adding or subtracting degrees to decide if it is a fever.  In reality, you can look at a child to know if they are sick.  The degree of temperature helps guide if they can go to school or daycare, not how you should treat the child.  Fevers in children are generally defined as temperatures above 100.4 F (38 C).

Fever is rarely dangerous, though parents often fear the worst.

This is the time of year kids will be sick more than normal.  With each illness there can be fever (though not always.)


What you can do:

• Be prepared at home with a fever reducer and know your child's proper dosage (especially with the recent dosing changes to acetaminophen!) 
• Use fever reducers to make kids comfortable, not to bring the temperature to normal.
• Have an electrolyte solution at home in case of vomiting. 
• Teach kids to wash their hands and cover coughs and sneezes with their elbows.  
• Stay home when sick to keep from spreading germs.  It is generally okay to return to work/school when fever - free 24 hours without the use of fever reducers.  
• Help kids rest when sick.
• If the fever lasts more than 3-5 days, your child looks dehydrated, is having trouble breathing, is in extreme pain, or you are concerned, your child should be seen.  A physical exam (and sometimes labs or xray) is needed to identify the source of illness in these cases.  A phone call cannot diagnose a source of fever.
• Any infant under 3 months or immune compromised child should be seen to rule out serious disease if the temperature is more than 100.5.

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