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Your Baby’s Temperature and Fever

A true fever is a cause for worry in the first few months of a baby’s life. That’s because the infant's immune system is immature and not as effective in fighting infections as it will be after three or four months living outside the womb.

It’s vital to learn how to correctly take your baby’s temperature and to understand what signifies a true fever.

What Is Considered a Fever for My Baby?

Most doctors say a baby has a fever if the temperature rises to 100.4 F or above when measured with a rectal thermometer. Take your baby’s temperature a few times when he or she is well to know his or her normal temperature.

What Causes a Fever in Babies?

There can be many causes for a baby’s fever, but the most common is infection. 

As in older children and adults, the body’s immune system senses the “foreign invader,” such as bacteria or a virus, and sends a chemical message to the brain, instructing it to crank up the body's heat. This has advantages. Some bacteria and viruses don’t like the higher temperature, so they are more easily destroyed by the immune system. In that way, fever is actually a friend: It lets you know that an infection may be brewing, and it helps protect against it.

Another possible cause of a higher-than-normal body temperature is being over-bundled with clothes in a relatively warm environment. The rule of thumb is to dress your baby in just one more layer of clothing than you are comfortable in.

When to Worry About Your Baby’s Fever

Any fever in the first months could indicate a significant infection requiring immediate attention. All children under age 2 months with a true fever need a medical evaluation. Call your doctor about fevers for at least the first four to six months of your baby’s life.   

At your baby’s next well check, ask your doctor about his or her own “fever policy” so you have a better idea about when your pediatrician wants you to call. But don’t hesitate to call your pediatrician when your baby has a fever and you’re worried -- take the better-safe-than-sorry approach if you’re concerned.

But fever is only part of the story. An even more important question is: does your newborn look unwell? If your baby shows any sign of being sick – for instance, irritability, listlessness, lethargy, poor feeding, respiratory distress, rash, vomiting, diarrhea -- contact your doctor, even if the temperature is not high enough to be called a fever.

WebMD Medical Reference

Reviewed by Renee A. Alli, MD on March 25, 2014
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