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
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.
The illness is probably not serious if your child:
- is still interested in playing
- is eating and drinking well
- is alert and smiling at you
- has a normal skin color
- looks well when his or her temperature comes down
And don't worry too much about a child with a fever who doesn't want to eat. This is very common with infections that cause fever. For kids who still drink and urinate normally, not eating as much as usual is OK.
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.)
As any parent knows, taking a squirming child's temperature can be challenging. But it's one of the most important tools doctors have to determine if a child has an illness or infection. The method you choose to take your child's temperature will depend on his or her age and how cooperative your child is.
If your child is younger than 3 months, you'll get the most reliable reading by using a digital thermometer to take a rectal temperature. Electronic ear thermometers aren't recommended for infants younger than 3 months because their ear canals are usually too small.
If your child is between 3 months to 4 years old, you can use a digital thermometer to take a rectal temperature or an electronic ear thermometer to take the temperature inside the ear canal. You could also use a digital thermometer to take an axillary temperature, although this is a less accurate method.
If your child is 4 years or older, you can usually use a digital thermometer to take an oral temperature if your child will cooperate. However, kids who have frequent coughs or are breathing through their mouths because of stuffy noses might not be able to keep their mouths closed long enough for an accurate oral reading. In these cases, you can use the tympanic method (with an electronic ear thermometer) or axillary method (with a digital 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.
To take a rectal temperature: Before becoming parents, most people cringe at the thought of taking a rectal temperature. But don't worry — it's a simple process:
- Lubricate the tip of the thermometer with a lubricant, such as petroleum jelly.
- Place your child:
- belly-down across your lap or on a firm, flat surface and keep your palm along the lower back
- or face-up with legs bent toward the chest with your hand against the back of the thighs
- With your other hand, insert the lubricated thermometer into the anal opening about 1/2 inch to 1 inch (about 1.25 to 2.5 centimeters). Stop if you feel any resistance.
- Steady the thermometer between your second and third fingers as you cup your hand against your baby's bottom. Soothe your child and speak quietly as you hold the thermometer in place.
- Wait until you hear the appropriate number of beeps or other signal that the temperature is ready to be read. Write down the number on the screen, noting the time of day that you took the reading.
To take an oral temperature: This process is easy in an older, cooperative child.
- Wait 20 to 30 minutes after your child finishes eating or drinking to take an oral temperature, and make sure there's no gum or candy in your child's mouth.
- Place the tip of the thermometer under the tongue and ask your child to close his or her lips around it. Remind your child not to bite down or talk, and to relax and breathe normally through the nose.
- Wait until you hear the appropriate number of beeps or other signal that the temperature is ready to be read. Write down the number on the screen, noting the time of day that you took the reading.
To take an axillary temperature: This is a convenient way to take a child's temperature. Although not as accurate as a rectal or oral temperature in a cooperative child, some parents may prefer to take an axillary temperature, especially for kids who can't hold a thermometer in their mouths.
- Remove your child's shirt and undershirt, and place the thermometer under an armpit (it must be touching skin only, not clothing).
- Fold your child's arm across the chest to hold the thermometer in place.
- Wait until you hear the appropriate number of beeps or other signal that the temperature is ready to be read. Write down the number on the screen, noting the time of day that you took the reading.
Whatever method you choose, keep these additional tips in mind:
- Never take a child's temperature right after a bath or if he or she has been bundled tightly for a while — this can affect the temperature reading.
- Never leave a child unattended while taking a temperature.
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 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 Larissa Hirsch, MD
Date reviewed: November 2007