What Is Fever?
Fever occurs when the body's internal "thermostat" raises the body temperature above its normal level. This thermostat is found in the part of the brain called the hypothalamus. The hypothalamus knows what temperature your body should be (usually around 98.6° Fahrenheit, or about 37° Celsius) and will send messages to your body to keep it that way.
Most people's body temperatures even change a little bit during the course of the day: It's usually a little lower in the morning and a little higher in the evening and can fluctuate as kids run around, play, and exercise.
Sometimes, though, the hypothalamus will "reset" the body to a higher temperature in response to an infection, illness, or some other cause. So, why does the hypothalamus tell the body to change to a new temperature? Researchers believe turning up the heat is the body's way of fighting the germs that cause infections and making the body a less comfortable place for them.
What Causes Fever?
It's important to remember that fever by itself is not an illness — it's usually a symptom of an underlying problem. Fever has several potential causes:
Infection: Most fevers are caused by infection or other illness. Fever helps the body fight infections by stimulating natural defense mechanisms.
Overdressing: Infants, especially newborns, may get fevers if they're overbundled or in a hot environment because they don't regulate their body temperature as well as older children. However, because fevers in newborns can indicate a serious infection, even infants who are overdressed must be evaluated by a doctor if they have a fever.
Immunizations: Babies and children sometimes get a low-grade fever after getting vaccinated.
Although teething may cause a slight rise in body temperature, it's probably not the cause if a child's temperature is higher than 100° Fahrenheit (37.8° Celsius).
When Can a Fever Be a Sign of Something Serious?
In the past, doctors advised treating a fever on the basis of temperature alone. But now they recommend considering both the temperature and the child's overall condition.
Kids whose temperatures are lower than 102° Fahrenheit (38.9° Celsius) often don't require medication unless they're uncomfortable. There's one important exception to this rule: If you have an infant 3 months or younger with a rectal temperature of 100.4° Fahrenheit (38° Celsius) or higher, call your doctor or go to the emergency department immediately. Even a slight fever can be a sign of a potentially serious infection in very young infants.
If your child is between 3 months and 3 years old and has a fever of 102.2° Fahrenheit (39° Celsius) or higher, call the doctor to see if he or she needs to see your child. For older kids, take behavior and activity level into account. Watching how your child behaves will give you a pretty good idea whether a minor illness is the cause or if your child should be seen by a doctor.
How Do I Know if My Child Has a Fever?
A gentle kiss on the forehead or a hand placed lightly on your child's skin is often enough to give you a hint that your child has a fever. However, this method of taking a temperature (called tactile temperature) is dependent on the person doing the feeling and doesn't give an accurate measure of temperature.
Use a reliable thermometer to tell if your child has a fever when his or her temperature is at or above one of these levels:
- 100.4° Fahrenheit (38° Celsius) measured rectally (in the bottom)
- 99.5° Fahrenheit (37.5° Celsius) measured orally (in the mouth)
- 99° Fahrenheit (37.2° Celsius) measured in an axillary position (under the arm)
But how high a fever is doesn't tell you much about how sick your child is. A simple cold or other viral infection can sometimes cause a rather high fever (in the 102°–104° Fahrenheit / 38.9°–40° Celsius range), but this doesn't usually indicate a serious problem. And serious infections may cause no fever or even an abnormally low body temperature, especially in infants.
Because fevers may rise and fall, a child with fever might experience chills as the body tries to generate additional heat as its temperature begins to rise. The child may sweat as the body releases extra heat when the temperature starts to drop.
Sometimes kids with a fever breathe faster than usual and may have a higher heart rate. You should call the doctor if your child is having difficulty breathing, is breathing faster than normal, or continues to breathe fast after the fever comes down.
Different Types of Thermometers?
Whichever type of thermometer you choose, be sure you know how to use it correctly to get an accurate reading. Keep and follow the manufacturer's recommendations for any thermometer.
Digital thermometers usually provide the quickest, most accurate readings. They come in many sizes and shapes, are available at most supermarkets and pharmacies, and are available in a range of prices. Although you should read the manufacturer's instructions to determine what method or methods the thermometer is designed for, many digital thermometers can be used for the following temperature-taking methods:
- oral (in the mouth)
- rectal (in the bottom)
- axillary (under the arm)
Digital thermometers usually have a plastic, flexible probe with a temperature sensor at the tip and an easy-to-read digital display on the opposite end.
Electronic ear thermometers measure the tympanic temperature — the temperature inside the ear canal. Although they're quick and easy to use in older babies and children, electronic ear thermometers aren't as accurate for infants 3 months or younger as digital thermometers and are more expensive.
Plastic strip thermometers (small plastic strips that you press against your child's forehead) may be able to tell you whether your child has a fever, but they aren't reliable for taking an exact measurement, especially in infants and very young children. If you need to know your child's exact temperature, plastic strip thermometers are not the way to go.
Forehead thermometers also may be able to tell you if your child has a fever, but are not as accurate as oral or rectal digital thermometers.
Pacifier thermometers may seem convenient, but again, their readings are less reliable than rectal temperatures and shouldn't be used in infants younger than 3 months. They also require the child to keep the pacifier in the mouth for several minutes without moving, which is a nearly impossible task for most babies and toddlers.
Glass mercury thermometers were once common, but the American Academy of Pediatrics (AAP) now says they should not be used because of concerns about possible exposure to mercury, which is an environmental toxin. (If you still have a mercury thermometer, do not simply throw it in the trash where the mercury can leak out. Talk to your doctor or your local health department about how and where to dispose of a mercury thermometer.)
How to Use a Digital Thermometer
A digital thermometer offers the quickest, most accurate way to take a child's temperature and can be used in the mouth, armpit, or rectum. Before you use one, read the directions thoroughly. You need to know how the thermometer signals that the reading is complete (usually, it's a beep or a series of beeps or the temperature flashes in the digital window on the front of the thermometer).
First, turn on the thermometer and make sure the screen is clear of any old readings. If your thermometer uses disposable plastic sleeves or covers, put one on according to the manufacturer's instructions. Remember to discard the sleeve after each use and to clean the thermometer according to the manufacturer's instructions before putting it back in its case.
Helping Kids Feel Better
Again, not all fevers need to be treated. And in most cases, a fever should be treated only if it's causing a child discomfort. Here are ways to alleviate symptoms that often accompany a fever:
- If your child is fussy or appears uncomfortable, you can give acetaminophen or ibuprofen based on the package recommendations for age or weight. If you don't know the recommended dose or your child is younger than 2 years, call the doctor to find out how much to give. Remember that fever medication will usually temporarily bring a temperature down, but it will not return it to normal — and it won't treat the underlying reason for the fever. (Unless instructed by a doctor, never give aspirin to a child due to its association with Reye syndrome, a rare but potentially fatal disease.) Infants under 2 months old should not be given any medication for fever without being evaluated by a doctor. If your child has any medical problems, check with the doctor to see which medication is best to use.
- Giving a sponge bath can make your child more comfortable and help bring the fever down. Use only lukewarm water; cool water may cause shivering, which actually raises body temperature. Never use alcohol (it can cause poisoning when absorbed through the skin) or ice packs/cold baths (they can cause chills that may raise body temperature).
- Dress your child in lightweight clothing and cover him or her with a light sheet or blanket. Overdressing and overbundling can prevent body heat from escaping and can cause a temperature to rise.
- Make sure your child's room is a comfortable temperature — not too hot or too cold.
- Offer plenty of fluids to avoid dehydration — a fever will cause a child to lose fluids more rapidly. Water, soup, ice pops, and flavored gelatin are all good choices. Avoid drinks containing caffeine, including colas and tea, because they can cause increased urination.
- If your child also is vomiting and/or has diarrhea, ask the doctor if you should give an electrolyte (rehydration) solution made especially for kids. You can find these solutions at pharmacies and supermarkets. Don't offer sports drinks — they're not designed for younger children, and the added sugars may make diarrhea worse. Also, limit your child's intake of fruits and apple juice.
- In general, let your child eat what he or she wants (in reasonable amounts) but don't force eating if your child doesn't feel like it.
- Make sure your child gets plenty of rest. Staying in bed all day isn't necessary, but a sick child should take it easy.
- It's best to keep a child with a fever home from school or child care. Most doctors feel that it's safe to return when the temperature has been normal for 24 hours.
When to Call the Doctor
The exact temperature that should trigger a call to the doctor depends on the age of the child, the illness, and whether the child has other symptoms with the fever.
Call your doctor if you have an:
- infant younger than 3 months with a temperature of 100.4° Fahrenheit (38° Celsius) or higher
- older child with a temperature of higher than 102.2° Fahrenheit (39° Celsius)
Call the doctor if an older child has a fever of less than 102.2° Fahrenheit (39° Celsius) but also:
- refuses fluids or seems too ill to drink adequately
- has persistent diarrhea or repeated vomiting
- has any signs of dehydration (urinating less than usual, not having tears when crying, less alert and less active than usual)
- has a specific complaint (i.e., sore throat or earache)
- still has a fever after 24 hours (in kids younger than 2 years) or 72 hours (in kids 2 years or older)
- has recurrent fevers, even if they only last a few hours each night
- has a chronic medical problem such as heart disease, cancer, lupus, or sickle cell anemia
- has a rash
- has pain with urination
Seek emergency care if your child shows any of the following signs along with a fever:
- inconsolable crying
- extreme irritability
- lethargy and difficulty waking
- rash or purple spots that look like bruises on the skin (that were not there before the child got sick)
- blue lips, tongue, or nails
- infant's soft spot on the head seems to be bulging outward or sunken inwards
- stiff neck
- severe headache
- limpness or refusal to move
- difficulty breathing that doesn't get better when the nose is cleared
- leaning forward and drooling
- abdominal pain
Also, ask your child's doctor for his or her specific guidelines on when to call about a fever.
Fever: A Common Part of Childhood
All kids get fevers, and in the majority of cases, most are completely back to normal within a few days. For older infants and children (but not necessarily for infants younger than 3 months), the way they act is far more important than the reading on your thermometer. Everyone gets cranky when they have a fever. This is normal and should be expected.
But if you're ever in doubt about what to do or what a fever might mean, or if your child is acting ill in a way that concerns you even if there's no fever, always call your doctor for advice.
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