Why does a fever seem to spike at night?

April 30, 2018 Elizabeth Meade, MD



Like ghosts, car alarms, and unexpected phone calls, fevers are often worse at night. 

The same is often said about asthma, arthritis, and the flu. And although heart attacks commonly occur in the morning, researchers believe they are frequently triggered by night-time happenings in the body.

Health care professionals have known this about illness for many years, anecdotally. But science is beginning to offer some explanation and validation for the theory. There’s even a field of study devoted to understanding how time of day affects our health—chronobiology.

What is fever?

The primary symptom of fever is abnormally high body temperature. 

Normal body temperature for an adult can range anywhere from 97 F to 99 F. Children have a slightly higher range, approximately 98 F to 100 F. However, adults are much more tolerant of temperature spikes than children, and have more fully functional immune systems. With children—especially babies—even a slightly elevated temperature can signal something more serious.

In addition to a high temperature, symptoms of fever can include shivering and sweating, headache, muscle ache, loss of appetite, and general fatigue. In  some cases, children under 5 may suffer seizures during high fever spikes —alarming for parents, but not usually life-threatening. 

It’s important to remember that fever itself is not a disease. In fact, it’s the exact opposite—a sign that the body’s immune system is fighting off a bacterial or viral infection — although it can be a cause for serious concern in certain circumstances: for example, urgent medical evaluation is needed if an infant less than two months of age is running a fever greater than 100.4 degrees Fahrenheit, or if anyone with a compromised immune system spikes a fever.

Is “night fever” really worse?


There are some fairly obvious explanations for “night fever”—the tendency for fever symptoms to be magnified during the evening hours. 

First, it’s normal for body temperature to creep up at night, adding proverbial fuel to the fire. This is often compounded by well-meaning parents or caregivers swaddling their infant under piles of blankets. Incidentally, it’s precisely because of this natural ebb and flow of body temperature that health care professionals don’t declare a fever broken in the morning just because someone suddenly seems symptom-free. Instead, they often wait until fever has been absent for 24 hours to celebrate.    

There’s also the undeniable boredom effect. During the day—even if you have a fever—you tend to be more active or at least distracted by visitors, making sure you’re drinking lots of fluids and getting enough rest. At night, it’s just you, the four walls, and your fever—so you have more time to think about how miserable you feel. And, guess what, that makes you feel more miserable. 

But probably the main reason fever seems worse at night is because it actually is worse. The inflammatory response mechanism of the immune system is amplified. Your immune system deliberately raises your body temperature as part of its strategy to kill the virus attacking you. That’s what triggers the alternating hot flashes and chills—the classic fever effect. 

There’s one other element that we don’t quite fully understand, but it seems to be important. We know that two key hormones – cortisol and adrenaline – are suppressed when we sleep. From extensive studies on asthma management, we have learned that when the level of these hormones is reduced at night, it’s harder for asthmatics to breathe. Researchers believe this restriction also exacerbates fever symptoms at night

When you or your family members have a troubling fever, trust your instincts if you think something is wrong and call your pediatrician or family doctor for advice. And remember, always call a doctor if a young infant has a fever of more than 100.4. Find a skilled Swedish doctor in our provider directory or call 1-800-SWEDISH (793-3474).

Elizabeth Meade, MD, is chief of pediatrics at Swedish.

Recommended for you:
Fever in kids: Myths and tips
What to do if your child has a febrile seizure

This information is not intended as a substitute for professional medical care. Always follow your health care professional's instructions.


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