Why do Fevers happen at night?

March 11, 2017

As a pediatrician the question, “Why do they always get fever at night?” is heard frequently. Other than your child’s prankster heart knowing the doctor’s office is closed at 3am and how much you love to worry there is an actual reason why a temperature will spike in the wee hours.

We all know that a normal body temperature is 98.6 Fahrenheit right? Wrong! 98.6 F is an average body temperature. Our body will naturally fluctuate a degree in each direction throughout the day. This obviously means that a normal body temp can range from 97.6-99.6 F right? Sorry, wrong again. These temperatures are the average. Body temps actually follow one of those bell shaped curves. Yeah, I tried to skip those classes in high school too. About 84% of people fall in that curve with 7% of people falling above that range and 7% falling below it. Before you think your child has a temp it would be amazing to know what your child’s temp is normally. As physicians have determined that a fever is anything over 100.4.

Back to the question of, WHY at night? Part of the reason is you may not have seen or touched your child all day. Sometimes a little kid can be pretty slimy or sticky. Appearing perfectly normal they may have had a fever during the day, but until you touch them you didn’t notice it. It is true that they may have higher temps during the night and early morning. The reason has to do with the complicated subject of our normal body steroids. Our normal body steroids tend to dip at night between 9 pm and 4-5 am. This dip in our steroid level is the reason our temps go up. Just FYI this dip is also responsible for croup and asthma being worse at night and the reason that most deaths occur during these hours.

You have accidently learned something new! What you’ve learned is good information but it doesn’t really change anything. Though parents easily freak out over a high temp doctors very rarely do. We are more concerned that they have a fever rather than how high it is. Though we will try to believe a parent’s estimated prediction of their child’s now dissipated fever (please use an actual thermometer) we know that the temp naturally goes down during the day when we are going to be seen at an appointment. Unless there is another medical situation an ER visit caused by a fever is rare. The exception to this is if you have a baby less than two months old (we consider this fever an emergency) or if you have recently had a surgical procedure.