Sleep is critical to our survival, not only physically but also mentally. Recent research has shown just how detrimental losing just thirty minutes of sleep each night can be. Therefore you should be trying to sleep as much as possible.
However, if you are getting an extremely high body temperature while sleeping, you might wake up, experience less deep REM sleep and feel less refreshed the next morning. A common question we see is, “why does my body temperature rise at night“? This rise can happen for a variety of reasons. Often it can disrupt your sleep and make you feel tired the next day.
Why Is Body Temperature Important At Night?
You might have heard that each evening your body produces a chemical called melatonin which makes you feel tired and ready to sleep. But what you might be unaware of is that your body temperature begins to decline as well, which tells your body to rest. The temperature of your internal body is critical to sleeping.
Each day your temperature shifts between roughly 96.8 and 100.4 degrees Fahrenheit, given a normal circadian rhythm you will begin to drop in temperature around 8 pm through until 5 am. Research has shown that not only is there an optimal temperature for sleep, somewhere between 60 and 68 degrees, but the rate of change is also vital.
Sleep occurs when the core temperature is dropping at the quickest rate, i.e., the loss of body heat is maximal. This change in temperature signals to your body that it’s time to sleep. If you fail to let your body heat drop at all, particularly into the acceptable range which for many of us is far cooler than we usually keep our rooms, you will struggle to fall asleep and won’t have long deep REM cycles.
What Causes Changes In Body Temperature?
Humans can thermoregulate themselves, meaning they can maintain their body temperature. We can do this by balancing our heat absorption, production and loss to ensure that we are at an optimal level for our bodies to function. Even small variations can be disadvantageous and eventually become fatal.
We have two different zones to regulate our heat, the core temperature, and the shell temperature. The abdominal, thoracic and cranial cavities are the most important areas because they contain our vital organs. This area is known as the core and has a separate temperature. The shell is the skin, subcutaneous tissues, and muscles.
The shell has its temperature too, but unlike the core, the shell temperature is more affected by the external temperature than it is from the brains conscious choices. The core is the most important part of our body, and therefore it uses the shell to either conserve or release heat whenever it needs to.
When the core temperature gets too high, blood vessels which are located in the skin will dilate, allowing more blood flow, much of which is closer to the skin. Heat is lost through this blood flow and the walls of the skin. We also produce sweat, as you’ll notice when you exercise and raise your core body temperature.
Sweat beads on the surface of our skin and when it evaporates it takes lots of the heat from the body with it, cooling us down. On the contrast, when we are too cold the blood vessels contract and minimize heat loss by directing the blood flow to our organs and away from our skin and limbs.
Body Temperature Throughout The Day
It’s not just in the night that body temperature changes, it’s constantly changing throughout the day. Typically, your body starts somewhere around your baseline of 98.6 when you first wake up and over the course of the morning into the early afternoon it will increase slowly until it reaches roughly 100.4 degrees Fahrenheit.
Scientists have shown that the higher our body temperature, the more awake and alert we feel. You can try this yourself when you workout and increase the core temperature you will feel bright and awake, even though you should be tired from the exercise. Around two to three in the afternoon your temperature temporarily drops, suggesting that we were designed to have an afternoon nap.
After this napping period, body temperature rises once again until it peaks in the late afternoon or early evening. From here it slowly drops, reaching maximal heat loss at the point where you should be going to sleep. It will continue to drop throughout the night until a few hours before you wake, which is when it starts to increase again to wake you up and make you feel alert.
Our body has a natural body clock that is only slightly longer than the length of a day, but we’ve evolved to line up very well with the cycle of the sun. As a result, we are hottest and therefore most alert when the sun is at its peak, and our body temperature begins to drop very rapidly once the sun disappears, stimulating melatonin production and making us ready for bed.
Why Is My Body Temperature Rising While Sleeping?
Let’s start by saying this; your core body temperature should only rise while sleeping in the final few hours of sleep. Your shell temperature, on the other hand, can rise and fall depending on the external environmental temperature.
Sickness And High Body Temperature At Night
There is an exception to this rule, and that’s for women that are experiencing menopause. This period of life can send the body into shock whereby core temperature might not line up with your circadian rhythm. If you’re sometimes experiencing hot flushes in the day, it’s possible that you’re also getting these while sleeping.
If you’re not a woman, nor experiencing other menopausal symptoms, it’s possible that you are sick. Flu and other more serious conditions can cause body temperature to rise as it tries to fight off the problem. These conditions can cause to wake up in the middle of the night sweating and burning up.
As with menopause, you should be able to correlate this nighttime increase in body temperature to daytime warmness and other sickness symptoms. If neither of these factors is the case, it could be that your environment is too hot or the way that you are tracking body temperature is inaccurate.
Scientists recommend that we keep our rooms between 60 and 68 degrees throughout the evening, but even if this is the case, you might be adding extra heat, especially with clothing and sheets. If you’re regularly waking up in the middle of the night and feeling hot, or tracking your temperature and seeing it rising throughout your entire sleep, you are almost certainly keeping yourself too warm.
Although you might be reluctant to throw away the sheets because they are cozy and comfortable, you need to drop the room temperature down to the recommend range and reduce the heat. You can do this by sleeping naked, minimizing the sheets in use and reducing pillows to one thin (not dense) pillow.
Poor Temperature Tracking
It’s also possible that you’re not experiencing an increase in body temperature but the method of tracking is inaccurate. If you’re using a watch or other wearable device, it’s tracking shell temperature which while related to core body temperature, is more indicative of a hot environment.
Similarly, if another person such as your partner is telling you that you are hot or you wake up at night feeling warm, this isn’t necessarily a confirmation that your core body temperature is rising at all.
Reducing Your Nighttime Temperature and Sleeping Better
Research has consistently shown that body temperature is critical to achieving a deep, meaningful and restorative sleep. Unfortunately, in the era of houses, running water and comfortable beds, many of us choose far too much comfort, and this increases our body temperature, ruining our sleep.
To combat this, especially for those of us who have increasing body temperatures at night or who wake up sweating, you need to make some sacrifices. Often these changes can be tough at first, but you quickly become accustomed to them as you’ll feel more refreshed the next morning and your body will become used to the cooler feeling of the evening.
Choose Thinner Or Fewer Sheets
Perhaps the most common mistake that is made, especially among those with less body fat, is compensating with multiple thick sheets. Unless it’s a very cold night, the chances are that there is no need to sleep with more than a single thin duvet sheet.
While it can feel comfortable to use more because you get a thick layer to wrap yourself in, those thick sheets prevent air circulation and trap air against your body where it gets hot and prevents heat loss. This air can cause you to overheat, waking you up in sweats or causing an unfulfilling sleep.
Use Fewer Pillows
Pillows aren’t quite as harmful as excessive sheets, but many of us use multiple pillows on our bed, stacked on top of each other to create a huge rest for our head. Again, these prevent air circulation through the bed, trap extra heat and generally increase the temperature of the bed, which reduces heat loss through your shell, preventing the core from cooling down.
The problem of pillows is particularly bad for those of us that use memory foam or dense foam pillows because they have very little breathability. While traditional feather pillows are primarily filled with air, the foam is incredibly dense and very little air can get through it. This type of pillow prevents cooling and can cause you to overheat, especially in the head and upper back.
Even if you’re only using a single sheet and pillow, the clothes that you’re wearing to bed might be preventing cooling through your shell. To fix this, you should try reducing the clothes that you wear to sleep, or simply sleep naked.
Doing so will allow your body to cool down quicker and more easily. You might imagine that this will cause you to sweat more onto the sheets, but reducing the clothing you wear should minimize the amount you sweat, thereby diffusing the problem from the root.
Reduce Room Temperature
If after all of these changes you’re still waking up hot in the middle of the night or feel that your body temperature is continuing to rise, you should drop the temperature of your room further. While 60 to 68 is the guideline, you might need a lower temperature if you happen to sleep hot at night, which is common among those who are overweight or who have large amounts of muscle.
Taking the temperature down to 55 or even 50 degrees can have a massive difference. After all, if you’re going to sleep with bed sheets, you should feel like you need them, rather than using them purely for the sake of it or physical comfort.
Take a Warm Bath Before Bed
Hotness can make it hard to fall asleep, and if this is the case for you, you might consider taking a warm bath shortly before you want to go to sleep. This idea sounds crazy, right? But taking a warm, but not hot bath, will dilate all of your blood vessels so that when you get out of the bath, your body temperature will plummet, far below what it was when you first got into the bath.
This handy hack can be a lifesaver and is precisely why it’s recommended by so many bloggers and health experts. Not only does it take you away from screens and distractions, allowing melatonin production and stress reduction, but it drastically decreases your body temperature to allow you to fall asleep quickly.
Don’t Eat, Exercise or Use Caffeine Before Bed
There are three other factors that you might consider, food, exercise, and caffeine. All of these will cause your core body temperature to increase by varying degrees, and when they are done within the final two hours before bed, they can prevent you from sleeping and cause your core body temperature to continue to rise. Instead, try to eat your final meal no less than three hours before bed, use caffeine more than eight hours before and exercise three hours before bed.