Unfortunately, babies sometimes get sick, and a fundamental clue that things are amiss is a fever--a body temperature that's higher than normal. Most pediatricians consider any thermometer reading above 100.4º F a sign of fever. A fever can be alarming, but except in the case of heat stroke (a dangerous rise in body temperature caused by a sweltering environment, like a car with the windows rolled up in August), a fever by itself isn't an illness. It's the immune system's way of signaling that it's working to fight an infection.

Still, fever is often the first sign of illness, and your baby's temperature reading--coupled with your baby's other symptoms (if any)--will help your pediatrician diagnose why he has a fever. But accuracy is key. For babies under 3 months old, especially, every tenth of a degree counts. The difference between a temp of 100.3º F and 100.4º F, for example, can determine whether you stay home or take your baby to the emergency room. Any fever in this age group is typically considered an emergency. If your baby is under 4 weeks old, and has a fever of 100.4º F or greater, call your pediatrician immediately. A baby that young with a fever of 100.4º F or higher will most likely need to be hospitalized to rule out serious infection. For babies 4 weeks to 3 months old, it's still an emergency that needs prompt medical attention.


Rectal Thermometers: Tops for Temps

Due to the toxic risks of mercury, digital thermometers have replaced the glass thermometers you may have grown up with. In fact, if you have a mercury thermometer, get rid of it, advises the American Academy of Pediatrics (AAP). But don't just throw it away. Your doctor or local health department can tell you how to dispose of it properly.

Digital thermometers are easy to read and they don't expose your baby to the mercury that's in a glass thermometer, which is dangerous if the thermometer breaks. Get a digital thermometer that can be used rectally and orally (for later on). You can also take a baby's temperature by mouth, by ear, on the forehead, or under the arm, but the AAP considers rectal readings to be the most precise way to take a temperature in infants and children younger than 3. (With the model of forehead thermometer we tested, which required pressing a button and rolling the thermometer over a child's forehead, the results weren't precise.) After your baby's first birthday, your pediatrician may allow you to use a different temperature-taking method, so be sure to ask what's acceptable at that point, if you want to switch.

A popular option you'll see in stores and online is digital ear (tympanic) thermometers, which measure body temperature inside the ear. "They aren't recommended for young children because there are lots of chances for error," says Paul Horowitz, M.D., medical director of Pediatric Clinics Legacy Health System in Portland, Ore. We've found that you have to align them in the ear canal perfectly to be accurate. Temps taken orally, with a pacifier thermometer, may seem to be another way to go. But oral thermometers tend to be as much as 1º F lower than rectal thermometers and aren't considered as accurate for children under age 3.


Shopping Secrets

Check features. Simple as digital thermometers are, some have bells and whistles that you might find convenient--beeps that tell you when they're in the right spot or when they're finished, or soft or curved tips.

Price and performance don't necessarily correlate. Extrapolating from our recent tests of oral, ear, and forehead thermometers in 24 adults and 21 children ages 5 to 14, we found you don't always get what you pay for. Thermometers can be pricey, but the best cost less than $15.

Think long-term. Since you'll probably be changing temperature-taking methods soon, go with a digital thermometer that can be used rectally and orally.

Ask your pediatrician for a recommendation. Your pediatrician may have a preferred brand, so be sure to ask at your next visit.


What's Available

Major brands of digital thermometers are, in alphabetical order: BD Digital (www.bd.com), Bébé Sounds (www.bebesounds.com), Omron (www.omron.com), Safety 1st (www.safety1st.com), Summer Infant (www.summerinfant.com), The First Years (www.thefirstyears.com), and Vicks (www.vicks.com). Digital thermometers retail from $3.79 to $34.99. Digital thermometers are available at leading pharmacy and baby product sites such as www.amazon.com, www.buybuybaby.com, www.cvs.com, and www.target.com.


Recommendations

For your baby's first thermometer, go with an inexpensive digital model that can be used rectally, and later, orally. Look for an LCD display that's easy to read and a start button that's easy to press. But don't be swayed by digital thermometers that claim to take a reading in an instant. A reading in 20 to 60 seconds is sufficient.

THERMOMETERS FOR THE FUTURE At around age 4 or 5, when your child is old enough to hold a thermometer under his tongue, with his mouth closed, without biting, you can use an oral thermometer. In our recent test of eight oral, ear, and forehead thermometers in adults and children over age 5, the oral ones proved most accurate overall; a digital oral thermometer is the best choice for an adult or child over age 3. Besides the BD Digital Accu-Beep ($10), the Vicks Comfort-Flex ($13), and the Omron 20 Seconds Digital ($13) mentioned in our Ratings, which will last you beyond babyhood, the Timex oral (the only one that announces its results by speaking), $18, is another very good choice for preschoolers and the rest of the family.