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  • Go to Brilliant.org/SciShow to learn more.

  • Being sick sucks.

  • But you might have noticed it often sucks more at night.

  • Maybe you can push through the day feeling just a little toasty

  • and gross, but after sunset, you're on a one-way bus to Fever Town.

  • And that wasn't your imagination.

  • Fevers do often rise at night, and that's largely because

  • that's when our bodies naturally stoke their internal furnaces.

  • Your body temperature is controlled by your hypothalamus,

  • a small region at the base of your brain.

  • It can sense the temperature of the blood that passes through it,

  • and receives temperature information from your skin, too.

  • And it uses all this info, as well as chemical signals from your body,

  • to calibrate your internal temperature to a cozy 37 degrees C.

  • But even when you're totally healthy, it doesn't keep your body temperature completely stable throughout the day.

  • Instead, you fluctuate by up to half a degree Celsius in either direction

  • thanks to your body's circadian rhythmessentially your body's internal clock.

  • That rhythm is controlled by a tiny region of the hypothalamus

  • called the Suprachiasmatic Nucleus, or SCN for short,

  • which receives light and dark signals from nerve cells in your eyes as well as input from other parts of your brain.

  • Usually, these rhythms cause our body's temperature to dip

  • to its lowest point around 4 in the morning,

  • and then to the high end of the normal range around 6 at night.

  • And this daily cycle doesn't stop when you're sick.

  • So during fever, not only is your temperature elevated,

  • it's still subject to that upward swing in the evening.

  • And that's not all.

  • Circadian rhythms also influence your immune system.

  • You see, fevers are triggered by substances called pyrogens.

  • These can come from a few places.

  • White blood cells can release them into the bloodstream when they sense an intruder.

  • Or, might be emitted more directly by infected tissue or the pathogens themselves.

  • But wherever they're from, the effect is the same:

  • they tell the hypothalamus to ramp your thermostat up.

  • And because of that, the daily cycles of your immune system

  • could add to your nightly temperature spike.

  • You literally have more white blood cells at night, for example,

  • and studies have found some pyrogen levels also tend to spike in the evening.

  • Now, there are exceptions to this nightly fever pattern, of course.

  • Bacterial pneumonia and typhoid fever, for instance,

  • typically cause fevers that stay elevated all day

  • and night without that daily fluctuation.

  • And some kinds of malaria lead to fever spikes that occur on 2 or 3 day cycles instead of daily.

  • So keeping track of how your temperature changes over time

  • could help your doctor figure out what's got you feeling so crummy.

  • And in general, you should probably check your temperature at the same time every day

  • if you really want to know if you're getting better or worse.

  • The best time is probably somewhere between 6 and 8 pm,

  • since that's when your temp will likely be the highest.

  • Of course, I am not a doctor, so if you have

  • any concerns about a fever at any time of day,

  • you should definitely consult a healthcare professional.

  • And if you do find yourself stuck at home thanks to a particularly nasty bug, you might

  • as well do something fun with your downtime.

  • Like, take a course or two from Brilliant.org!

  • You see, learning doesn't have to be dull.

  • Brilliant offers a variety of engaging courses in math, science, and computer science that

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  • For example, their puzzle science course teaches physics the fun way by getting you to solve

  • puzzles about mirror reflections, laser tag, and making the perfect shot in a game of pool.

  • Right now, the first 200 people to sign up at Brilliant.org/SciShow will get 20% off the annual Premium subscription.

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Why Do Fevers Get Worse at Night?

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    Jerry Liu posted on 2019/09/18
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