Causes of Night Fever: Why It's Higher Later «

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Causes of Night Fever: Why It’s Higher Later

[Editor’s note: This article was originally hosted on, our sister site.
It’s now featured here as part of our new general-health section.]

by Emmanuel Rodriguez, M.D., M.P.H.

Q. Why does a fever sometimes get higher at night?

A. The answer to that is pretty simple: Body temperature, whether you’re sick or well, just gets higher later in the day. But the explanation behind that answer has to do with all sorts of things.

Three factors regulate your body temperature:

  1. A small gland at the base of the brain called the hypothalamus
  2. Your body’s vital functions (such as your muscle activity and heart rate)
  3. The temperature of your surroundings
Fever Cause: Your Inner Thermostat

The hypothalamus is your body’s built-in thermostat. By secreting hormones in small pulses, it communicates with your other vital organs, carefully regulating your body temperature close to a set temperature of 98.6 degrees Fahrenheit.

If you produce excess heat by exercising, your hypothalamus reduces your temperature by increasing the blood flow to your skin (basically, drawing more heat out of your body) and by making you sweat. On the other hand, if you go out into the cold, your hypothalamus tries to increase your temperature by causing you to shiver.

When you have a fever, the hypothalamus has reset your body temperature to one that’s higher than normal. It does this for an unclear reason. Some people think fever helps the body’s immune system fight the infection because some bacteria don’t thrive on higher temperatures.

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Why a Fever Is Higher at Night: Your Heat Cycle

Books adYour temperature usually follows a built-in 24-hour cycle. Its lowest point is between 3 and 6 a.m., followed by a peak between 4 and 11 p.m.

Two major factors regulate this cycle:

  1. Your hypothalamus has its own 24-hour hormone-secretion pattern. We don’t know the reason for this so-called circadian rhythm, but to some extent the day/night light cycle helps regulate it.
  2. The things the body does during the day (heartbeat, muscle movements, breathing) involve a release of heat energy, causing your core body temperature to warm up as the day progresses.

This explains why your temperature increases toward the end of the day under normal conditions. However, this cycle still happens when you have a fever. The difference is that now, the temperature elevation is more obvious since you’re already starting from a higher temperature than normal.

There are exceptions to this cycle. Outside factors that can dampen the evening temperature-elevation include older age; certain medical conditions, such as diabetes; and the use of some common drugs, such as acetaminophen (Tylenol) or aspirin—all of which affect the functioning of the hypothalamus.

Board certified in internal medicine,
 EMMANUEL RODRIGUEZ, M.D., M.P.H., is an infectious-disease specialist with NorthReach Internal Medicine Clinic in Marienette, Wis., and attending physician and hospital epidemiologist with Bay Area Medical Center.

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  • Atharv Dwivedi

    Hello, myself Atharv and I am suffering from viral fever for 5 days. 101to 103 is normal temp. Blood and urine test did not show anything. After takin med, I get relief only for 2 3 hours. Waiting for your reply

    • James Hubbard, MD, MPH

      Sorry but your doctors will know better what the problem is than I would.

  • C. James

    I have had a low grade fever (99.4-101.0) since April, mostly in the late afternoon 5:00PM til 11:00 PM, and fluxuating dailly. I have no other symthoms of ill health. I have had blood work done twice to follow up on the doctors suspensions of what it could be, and I’ve had a urinalysis to determine if it was a possible bladder infection, all is clear. What suggestions do you have of my next move in determining what’s going on with
    my body. I’m 72, have worked out for 27 years, not overweight and eat healthy.
    Please advise.

    • James Hubbard, MD, MPH

      First, see if you doctor has any suspicions. And remember that any temperature under 100.4 F orally may be normal. Also know that anyone’s temperature varies by a degree or two depending on the time of day. But, if it is above 100.4 and your doctor can’t give you a viable answer on why, perhaps it’s time to seek a second opinion from an internist. The three top reasons for fevers of unknown origin at your age are from some undiagnosed infection, some inflammatory disease like rheumatoid arthritis or lupus, and cancer.

  • Colleen

    Is there anything “natural” to reduce intermittent fever occurrence. I have dysautonomia and a connective tissue disease and can’t take NSAIDs at all because of losing one kidney and low function in the remaining one. I’m not worried about the fever more then just being a pest. Would love to know if there is a vitamin or supplement to try to help reduce the frequency.

    • James Hubbard, MD, MPH

      Warrm sponge baths can bring the fever down. Unproven, but possible herbs that some use for fever are feverfew tea or yarrow, although.

      It seems to me that with your poor kidney function, that you should be careful with anything. If something you take brings your fever down, it is affecting your body. And that, to me, is a medicine. Herbs, supplements, etc. can certainly be good but, unlike fda approved medicines, you can’t be sure the exact dose you’re getting. Sometimes that doesn’t matter so much but, in your case, it does. So, I’d ask your doctors about low-dose aspirin or acetaminophen. At least you know exactly what you’re getting. And, please, ask them about any “natural” remedies also. In addition, I’d read up thoroughly on anything you take so you know the proper dose, how to take it, interactions, and, especially, what effects it might have on your kidney.

  • Carisma Flores

    My son been having a fever of 101.5 to 100.2 for two night should I be worried his 4

    • James Hubbard, MD, MPH

      The question would be what’s causing the fever. If you don’t have a good idea, perhaps you should call your doctor. Here’s a link to another post which contains a link to some helpful guidelines from the American Academy of Pediatrics. Please check it out

      • Carisma Flores

        Thank you took him to urgent care but they said it a virus throat looks a Lil red no meds. Were prescribed, his ped. Wouldn’t take walk in his fever has broke but still has real bad cough doesn’t really want to eat drinking plenty fluids playing more but cough worry’s me

        • James Hubbard, MD, MPH

          A cough is often a symptom of a virus. And just because he has a virus doesn’t mean he can’t be very sick. I’m guessing you were given some suggestions, maybe acetaminophen to help him feel better, maybe a cool mist humidifier to keep his airways moist. Maybe some vapor rub to put in the humidifier. Also here’s a post on honey for coughs (but only to use for children 2 or older)

          • Carisma Flores

            No they didn’t tell me anything like that at urgent care it was r first time there since ped. Didn’t want to take him she just ask what I was giving him I said mucinex and she said to cont. With that check him asked if ever had bronchitis I said no and she said virus n that was it walk out I stayed there confused thinking she was going to swab or prescribed something but no

          • James Hubbard, MD, MPH

            There’s not much to do for most viruses other than drinking fluids, rest, and some of the things I mention. Antibiotics don’t help.

          • Carisma Flores

            He has blister in mouth is that from fever and when I took him shower in Luke warm water he was doing fine then started crying saying he couldn’t breath??

  • ladyty

    My two year old was diagnosed with the flu sunday, but she is still having a temperature off and on mostly at night, should I take her back to the emergency room?

    • James Hubbard, MD, MPH

      I can’t give you specific advice. In general fever with the flu lasts for several days. Much would depend on how she looks, is she drinking fluids, etc. If you have concerns, call her doctor. Here’s a link to one of a series of 4 posts I have but everyone is different and this is general information