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Everything You Need to Know About Fever

Normal highs and lows

A high temperature doesn't necessarily mean that a child is sicker than if he has a low one. "How he acts is a more accurate indicator of how ill he might be," says Anne Thiele, M.D., assistant professor of pediatrics at the University of Alabama School of Medicine, in Birmingham.

"If your baby is over four months, a little listless but isn't fussing much, and still seems interested in feeding, then a slight fever doesn't need medical attention."

In fact, in a child over 2 months of age, a temperature isn't even considered a fever until it's 100.4°F or higher. A child's normal body temperature is about 98.6°F, but it will fluctuate throughout the day, says Mark Stegelman, M.D., a pediatrician on staff with Children's Health Care of Atlanta. "A baby's temperature can be as low as ninety-seven degrees or as high as ninety-nine degrees and still be normal."

These variations are caused by a host of different factors, including the time of day, his activity level, how heavy his clothing is, or whether he's just had a warm bath. Temperature readings also depend on the type of thermometer. Most doctors consider a rectal thermometer to be the gold standard: Its readings are closest to core body temperature. Due to the different way bodies conduct heat, both ear and underarm thermometers can be off by a degree or two.

No matter which method you use, it's important to know your child's normal range so you have something to compare it with when he's sick, says Dr. Stegelman. As a reference, take his temperature just before 6 a.m., when body temperature is typically lowest, and again between 5 and 7 p.m., when it normally peaks.