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Fever

What is a Fever?

A fever is a body temperature over 100.4°F rectally. Do not add or subtract degrees when you tell us what your child's temperature is, just tell us what the thermometer says and how you took it (ear, forehead, armpit, oral, or rectal). Many parents worry about fevers, but the way a child looks and behaves is more important than how high the temperature.

When should I treat a fever?

If an infant is under 3 months of age and runs a fever, he should be seen as soon as possible.  If it is after office hours, please take your infant to the nearest pediatric urgent care (preferred) or local emergency room.  Do not use any fever reducing medications without doctor supervision under 3 months of age.

Older infants and children can usually be managed at home with fluids, rest, and possibly fever reducing medicines.  It is recommended to treat the fever with a fever reducer to make the child more comfortable, not to bring the temperature to normal.  If the infant/child has pain/discomfort, or the temperature is over 101F orally/under arm or 102F rectally, then use a fever reducer such as acetaminophen or ibuprofen.  See below for how to treat a fever.

What causes fever?

Fever in children is usually caused by infection, and most infections are viruses.  Fever also can be caused by environment temperatures being too high (or overbundled babies); dehydration; medications, poisons, or other chemicals; cancer; or overactivity.  

Most fevers are caused by a virus and last 1-3 days.  The first 24 hours fever might be the only symptom, but then other symptoms (runny nose, cough, vomiting, sore throat) usually begin.  During the course of fever the temperature may vary several degrees.  This is normal.  Do not be alarmed if the temperature goes up during the illness, unless the associated symptoms worsen.

When do I worry about fever?

Any infant under 3 months or child that is not up to date on immunizations is considered at risk for bacterial infections, and should be evaluated with a physical exam at the minimum, so should be soon as soon as possible.

For otherwise healthy infants over 3 months, current guidelines state to not treat a fever until it is 102°F unless it is causing symptoms.  Between 100°F and 102°F fevers are considered low grade and felt to be beneficial.   Temperatures over 102°F may cause discomfort, so treat the symptoms with Acetaminophen (or Ibuprofen if child is over 6 months - do not alternate).

A fever is a fever. Some kids get higher temperatures with every illness. Other kids seem to never run a fever when they're sick. The number on the thermometer does not make a child more or less sick. There is no "magic" number we worry more about. Over 106°F the temperature itself may be dangerous, and it is recommended to be seen immediately.

Most fevers are not dangerous, but actually a good sign of an intact immune system.  A fever is the body's response to an illness, usually viral.  We recommend treating a fever when the child is in pain or uncomfortable.  Letting the body run a fever "burns" off an illness more quickly.  There is not a temperature that we "worry more".  We watch the child for other signs of illness, not the thermometer reading.  If a child is dehydrated, in uncontrollable pain, having breathing difficulty, or not coherent, then we are concerned regardless of the temperature. Those children need to be seen as soon as possible. If a fever lasts longer than 3-5 days but the child does not show the above concerns, the child should be evaluated in their primary care office during business hours.

Again, the way a child looks and behaves is more important than how high the temperature.  We get many calls with parents worried about fever, asking how high is too high.  We never care as much about the thermometer as much as how your child is otherwise.  You will know when your child is sick and needs treatment without taking the temperature!

How do I treat a fever?

Acetaminophen (TylenolTM) is the best option for fever control in babies over 3 months.  For children over 6 months, you may use Ibuprofen (MotrinTM or AdvilTM).  See our Medications Page. Do not alternate Acetaminophen with Ibuprofen.  Remember that it takes 30-45 minutes for the medicine to work.  If one type does not seem to work, you can change to the other type when the next medication dose is due, as long as your child is over 6 months.  Acetaminophen is dosed every 4-6 hours, Ibuprofen every 6-8 hours.  If the fever climbs before the dose is due, do not give an extra dose.  Overworking the liver is much more dangerous than the fever.  Do not use Aspirin in children.  A bath in warm water is ok and will work faster than medicines, though won't work as long.  If the child is chilling, cover him.  If she feels hot, undress her.  Any child under 3 months or underimmunized with a fever should be evaluated by a physician.

Should I worry about brain damage from a high fever?

Brain damage usually does not occur until the temperature is over 106°F, which is rare. 

What are fever seizures?

Fever seizures are more common, but relatively harmless.  These happen as the body temperature changes rapidly, not at a certain level of temperature.  Children may have fever seizures between 6 months and 6 years of age.  Once a child has one, he may have another one.  If your child has a fever seizure, try to remain calm, look at the time it starts and stops (it always seems longer than it is), make sure your child will not hurt himself (i.e. fall off a bed or drown in the tub), and be seen by a physician to identify any treatable source of fever.  Call 911 if the seizure lasts more than 10 minutes.

How should I take the temperature?

Rectal temperatures are most accurate under 4 months of age, and under arm (axillary) temps are good enough for older infants and toddlers.  When a child can keep the thermometer under the tongue, an oral temperature is good.  We do not recommend the ear thermometers, pacifier thermometers or forehead thermometers.  It is important to tell your provider how a temperature was taken and what the thermometer said, and to not add anything to that number.  

What is a normal temperature?

Most people think of a "normal" body temperature as an oral temperature of 98.6°F.  Your temperature may actually be 1°F (0.6°C) or more above or below 98.6°F.  Also, your normal body temperature changes by as much as 1°F (0.6°C) 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.

A rectal or ear (tympanic membrane) temperature reading is 0.5 to 1°F (0.3 to 0.6°C) higher than an oral temperature reading.  A temperature taken in the armpit is 0.5 to 1°F. (0.3 to 0.6°C) lower than an oral temperature reading.

In most adults, an oral temperature above 100°F or a rectal or ear temperature above 101°F is considered a fever.  A child has a fever when his or her rectal temperature is 100.4°F or higher.  This is by convention, but in actuality children’s normal temperatures may be higher than adults so higher temperatures may actually indicate fever.  In general we consider a fever to be a temperature that makes someone uncomfortable.  It is not necessary to treat based on the thermometer reading.  It is important to treat when the child is uncomfortable.  The goal is not to lower the temperature to “normal”, but to make the child more comfortable.

A journal called Contemporary Pediatrics published an article in May of 2001, about normal body temperature.  The “normal” body temperature of 98.6°F was determined in 1868, by Carl Reinhold August Wunderlich, who measured body temperature in 25,000 (some say one million, but that is debated!) patients using a 22 cm-long thermometer.  There is even debate on the number 98.6°F., since it was converted from 37°C., which is inexact.

The most recent study quoted in this article was:  “What is fever?  Normal temperature in infants less than 3 months old” by Herzog and Coyne in Clinical Pediatrics (1993; 32(3); 142).  This study of 691 healthy infants under 3 months old found an average rectal temperature was 99.4 +/- 0.5.  

Using statistical calculations, they defined fever as the following:
 

• Newborn to 1 month--100.4°F
• 1-2 month--100.5°F
• 2-3 month--100.7°F

When should your child be seen?

• Appears very ill, is unusually drowsy, or is very fussy
• Has been in an extremely hot place, such as an overheated car
• Has additional symptoms such as a stiff neck (not just sore muscles), severe headache, severe sore throat, severe ear pain, an unexplained rash-especially if it looks like bruises under the skin, or repeated vomiting and/or diarrhea
• Has a condition causing immune suppression (such as sickle cell disease, cancer, or if on steroids)
• Has a seizure (convulsions, stiff and shaking and not responsive)
• If the fever lasts more than 5 days
• Is less than 3 months of age and the temperature is over 100.4F rectally
• Is not up to date with the recommended vaccine schedule and has a fever
• Be sure to tell any provider if your child is not up to date on all vaccines for age!  This increases the types of illnesses the provider must consider when evaluating your child.

For More:

• Fever Is...
• Fever Phobia
• If My Child's Temperature is Usually Low, How Do You Define Fever?
• Evolution of Illness
• Fever - How High is Too High?