Month 8 Worry: Is Fever Dangerous to My Infant?

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My phone rings in the middle of the night. An anxious parent is at the other end of the line: "My infant felt warm, I took her temperature, it's 102. What do I do now?" This is by far the most common emergency call I get. Will you be ready for your baby's first fever?

What's the Issue?

Almost all infants will have at least one episode of fever by their first birthdays. Some babies will have many. Fever is defined by most pediatricians as any temperature (rectal is still the gold standard for infants) at or above 100.5 (38 C). A febrile (what doctors call "feverish") infant is cranky, harder to console than usual, and naturally worrisome to parents.

Most parents I talk to are either worried about serious bacterial illness or that the height of the fever is dangerous to their baby. "Will my baby have a seizure?" "Will my baby suffer brain damage?" The short answer is this: fevers are short-lived, normal, and totally benign.

Consider the Numbers

Five percent of all children will have a seizure with fever during early childhood. There is nothing you can do to prevent it. This is a terrifying event to witness as a parent, but almost never medically dangerous. A seizure in an infant is tonic (involves muscle tensing or stiffening), clonic (involves shaking or rhythmic muscle movement), and generalized (infants are unconscious and unaware of their surroundings).

If your child has a seizure with or without a fever, dial 911 and let a physician sort out the cause. It is likely that many children have unrecognized febrile seizures in their sleep—ones parents never know about. Of those kids who do have febrile seizures, there is a 50 percent chance that they will have another before their fifth birthdays. Babies who have a second febrile seizure within 24 hours of their first are rare and require more intense medical work-up or observation.

Viral infection is, by far, the most common cause of infant fever. These fevers can last 72 hours and reach heights of 105+. An infant's body can handle temperatures of this height without any consequences. Brain damage is thought to occur at temps of 107 to 108. The most common cause of dangerously high infant temperatures (hyperthermia) is not infection (this almost never happens), but infants locked unattended in cars.

Parents of very young babies, please note: Call your clinician immediately, no matter what time of day or night, if an infant younger than three months has a temp of 100.5 or higher. Because of their immature age, these febrile infants have a three percent chance of serious bacterial illness, which warrants immediate attention.