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Being sick sucks.
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But you might have noticed it often sucks more at night.
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Maybe you can push through the day feeling just a little toasty
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and gross, but after sunset, you're on a one-way bus to Fever Town.
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And that wasn't your imagination.
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Fevers do often rise at night, and that's largely because
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that's when our bodies naturally stoke their internal furnaces.
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Your body temperature is controlled by your hypothalamus,
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a small region at the base of your brain.
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It can sense the temperature of the blood that passes through it,
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and receives temperature information from your skin, too.
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And it uses all this info, as well as chemical signals from your body,
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to calibrate your internal temperature to a cozy 37 degrees C.
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But even when you're totally healthy, it doesn't keep your body temperature completely stable throughout the day.
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Instead, you fluctuate by up to half a degree Celsius in either direction
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thanks to your body's circadian rhythm — essentially your body's internal clock.
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That rhythm is controlled by a tiny region of the hypothalamus
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called the Suprachiasmatic Nucleus, or SCN for short,
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which receives light and dark signals from nerve cells in your eyes as well as input from other parts of your brain.
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Usually, these rhythms cause our body's temperature to dip
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to its lowest point around 4 in the morning,
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and then to the high end of the normal range around 6 at night.
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And this daily cycle doesn't stop when you're sick.
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So during fever, not only is your temperature elevated,
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it's still subject to that upward swing in the evening.
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And that's not all.
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Circadian rhythms also influence your immune system.
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You see, fevers are triggered by substances called pyrogens.
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These can come from a few places.
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White blood cells can release them into the bloodstream when they sense an intruder.
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Or, might be emitted more directly by infected tissue or the pathogens themselves.
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But wherever they're from, the effect is the same:
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they tell the hypothalamus to ramp your thermostat up.
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And because of that, the daily cycles of your immune system
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could add to your nightly temperature spike.
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You literally have more white blood cells at night, for example,
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and studies have found some pyrogen levels also tend to spike in the evening.
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Now, there are exceptions to this nightly fever pattern, of course.
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Bacterial pneumonia and typhoid fever, for instance,
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typically cause fevers that stay elevated all day
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and night without that daily fluctuation.
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And some kinds of malaria lead to fever spikes that occur on 2 or 3 day cycles instead of daily.
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So keeping track of how your temperature changes over time
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could help your doctor figure out what's got you feeling so crummy.
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And in general, you should probably check your temperature at the same time every day
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if you really want to know if you're getting better or worse.
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The best time is probably somewhere between 6 and 8 pm,
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since that's when your temp will likely be the highest.
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Of course, I am not a doctor, so if you have
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any concerns about a fever at any time of day,
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you should definitely consult a healthcare professional.
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And if you do find yourself stuck at home thanks to a particularly nasty bug, you might
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as well do something fun with your downtime.
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Like, take a course or two from Brilliant.org!
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You see, learning doesn't have to be dull.
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Brilliant offers a variety of engaging courses in math, science, and computer science that
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are designed for ambitious, curious people.
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For example, their puzzle science course teaches physics the fun way by getting you to solve
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puzzles about mirror reflections, laser tag, and making the perfect shot in a game of pool.
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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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And if you do, you'll also be supporting SciShow—so thanks!