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 of 100.4 degrees F or higher 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 to diagnose the cause of a fever. But accuracy is imperative. For babies under 3 months old especially, every 10th of a degree counts. The difference between a temperature of 100.3 degrees F and 100.4 degrees 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 100.4 degrees F or greater, call your pediatrician immediately. A baby that young with a fever of 100.4 degrees 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.
Read more: What to do if your baby has a fever
For your baby's first thermometer, go with an inexpensive digital model. 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 quick enough.
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