# Why do fevers always seem to get worse at night? **URL:** \ **Category:** Factual Questions\ **Created:** [November 10, 2009, 1:45am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985 "2009-11-10T01:45:41Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Fetchund](https://avatars.discourse-cdn.com/v4/letter/f/b2d939/32.png) [@Fetchund](https://boards.straightdope.com/u/Fetchund)\ **Post date:** [November 10, 2009, 1:45am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/1 "2009-11-10T01:45:41Z")
This is getting me down. For the past 4 days, I’ve been “kinda” sick, mostly cold symptoms all during the day, but in the evening my temp goes up above 100, and I’m definitely feeling sicker. It isn’t a case of meds wearing off - I’m not taking anything. I keep thinking I can go back to work, but our workplace has instituted a strict “not until you’ve been fever free for 24 hours” policy, and I’ve got to say I agree. After tomorrow, however, I’m out of PTO, and that is going to hurt the pocketbook something fierce. So why am I being bamboozled all day? ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [November 10, 2009, 1:49am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/2 "2009-11-10T01:49:35Z")
I’ve always wondered that myself, so I’m bumping this. I kind of assume it’s because you’re worn out because you overdid it during the day, just because I always do that. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [November 10, 2009, 1:54am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/3 "2009-11-10T01:54:30Z")
It’s probably more productive to look at it as ‘why is my temperature lowest in the morning?’ And the answer to that is because your [cortisol](http://en.wikipedia.org/wiki/Cortisol) levels are higher in the morning. Among other things, the hormone cortisol acts to lower body temperature. Phrased differently, of course, your fever is highest at night because that’s when your cortisol levels are lowest. From [the cite above](http://en.wikipedia.org/wiki/Cortisol), "The amount of cortisol present in the blood undergoes diurnal variation, with the highest levels present in the early morning . . . ". ---
**Author:** ![Yarster](https://avatars.discourse-cdn.com/v4/letter/y/7c8e57/32.png) [@Yarster](https://boards.straightdope.com/u/Yarster)\ **Post date:** [November 10, 2009, 1:55am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/4 "2009-11-10T01:55:21Z")
I wish I had an answer for you as I’ve had the same problem. I can go all day with just the sniffles, but at night, it’s sweating through the sheets and feeling like someone threw a bucket of water on me. I have two theories on this: Theory #1 is that when you’re relaxed at night, your blood pressure drops, your defenses are probably down, and the virus is getting the better of you, hence the need to ratchet up the heat. I assume during normal “walking around” or waking hours, you have enough blood flow and other natural bodily combatants that the body doesn’t need to fight as hard, and there’s less fever. Theory #2 is that I’m full of crap and it’s exactly the same. The difference is that when you’re awake, you take Dayquil, drink some cold water, and are generally doing more to actively fight the fever. ---
**Author:** ![Fetchund](https://avatars.discourse-cdn.com/v4/letter/f/b2d939/32.png) [@Fetchund](https://boards.straightdope.com/u/Fetchund)\ **Post date:** [November 10, 2009, 2:04am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/5 "2009-11-10T02:04:21Z")
OK, that article is great, but I’m confused on a few things - how can sleep deprivation increase cortisol levels, if sleep increases cortisol levels? and can this > [@](#): > > It has anti-inflammatory effects by reducing histamine secretion and stabilizing lysosomal membranes. The stabilization of lysosomal membranes prevents their rupture, thereby preventing damage to healthy tissues. explain why my nose is always stuffiest in the evening? I thought I might be slightly allergic to something at home. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [November 10, 2009, 2:21am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/6 "2009-11-10T02:21:31Z")
> [@Fetchund](#): > > OK, that article is great, but I’m confused on a few things - how can sleep deprivation increase cortisol levels, if sleep increases cortisol levels? Are you sure it says that sleep increases cortisol levels? With respect to stuffy noses, I don’t know for sure, but it’s a good bet that more than cortisol levels influence nasal congestion ---
**Author:** ![Fetchund](https://avatars.discourse-cdn.com/v4/letter/f/b2d939/32.png) [@Fetchund](https://boards.straightdope.com/u/Fetchund)\ **Post date:** [November 10, 2009, 2:52am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/7 "2009-11-10T02:52:16Z")
Ah, I need to practice reading for comprehension. I’m going to use the excuse that I’m sick… So, \*\*diurnal rhythms \*\*effect cortisol levels - so even if I didn’t sleep, my cortisol levels would be higher in the morning. Now I need to figure out why that would be a useful adaptation - but for now, I’m going to follow those rhythms and zonk out. Thanks, **KarlGauss**! ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [November 10, 2009, 3:27am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/8 "2009-11-10T03:27:18Z")
I doubt the reason is anywhere as simplistic as “well your cortisol is low.” First of all, the body manufactures the fever because it wants to (not because any germ forces it to). We don’t know exactly why it wants to (and it doesn’t initiate a fever for most infections), nor what sort of fever strategy would maximize the body’s goals. Apparently, the body believes that a fever before bedtime will do you good. We can only speculate why. Maybe so you’d go get some rest. Note, that the fever is highest before bedtime. At “night,” ie while sleeping, body temps drop. ---
**Author:** ![ToeJam](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@ToeJam](https://boards.straightdope.com/u/ToeJam)\ **Post date:** [November 10, 2009, 3:40am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/9 "2009-11-10T03:40:24Z")
> [@Fetchund](#): > > OK, that article is great, but I’m confused on a few things - how can sleep deprivation increase cortisol levels, if sleep increases cortisol levels? Stress increases cortisol levels. So sleep deprivation = stress on your body. Also, Cortisol tends to decrease your immune system/function. That’s why people who tend to get stressed out and such tend to get sicker. It’s that extra stress that produces more cortisol that basically helps to wear down the body. Higher cortisol = immune suppression. That’s one reason you don’t want to give sicker people cortisol creams for long term usage, because over time you can decrease their immune system even further. ---
**Author:** ![ToeJam](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@ToeJam](https://boards.straightdope.com/u/ToeJam)\ **Post date:** [November 10, 2009, 3:44am UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/10 "2009-11-10T03:44:39Z")
> [@Alex\_Dubinsky](#): > > I doubt the reason is anywhere as simplistic as “well your cortisol is low.” > > First of all, the body manufactures the fever because it wants to (not because any germ forces it to). . The body produces fevers, which is certainly true, but there are plenty of germs that use this very method to help compromise your body as well. Fevers can be caused by anaphylotoxins and endogenous pyogens- factors such as TNF-alpha, and IL-1, which is all good and well. However, there are also EXOGENOUS pyogens which are produced by bacteria to induce fevers as well. Such examples are gram negative bacteria have LPS proteins that make up their gram negative walls. This stuff basically is the same thing as TNF-Alpha, and IL-1, if it gets out into the body (usually by the lysis of the bacteria or sometimes by shedding) that can induce a fever response. Fevers can be produced by the body to help contain an illness, however, there are plenty of bugs that have evolved to use this method to help further their own goals as well. ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [November 10, 2009, 2:49pm UTC](https://boards.straightdope.com/t/why-do-fevers-always-seem-to-get-worse-at-night/516985/11 "2009-11-10T14:49:26Z")
> [@Alex\_Dubinsky](#): > > Apparently, the body believes that a fever before bedtime will do you good. We can only speculate why. Maybe so you’d go get some rest. I don’t think it’s safe to assume there is a reason. Just because the body does something doesn’t mean it’s evolved specifically to do that thing - it could be a side effect of other “goals” of the body.