*Disclaimer: The written article is based on a summary of existing scientific literature on the topic of infrared saunas. The article is for educational purposes and the information provided below cannot be taken as a promise to help with acute health problems or diseases. The claims in the article are backed by 26 scientific references. All references are numbered. You can access the text of the reference by clicking on the number.
For that reason, we've decided to write a blog post about why you may not sleep after infrared sauna session.
Let's take a look at why some people sleep more poorly when planning an infrared sauna session just before bed, and, how to fix the problem.
First, let's cover some basics about sleep quality:
Sleep Quality 101
During sleep, your body moves through different sleep stages (1; 2; 3). Those sleep stages are made up of different non-REM parts and a REM part. REM sleep - which stands for "Rapid Eye Movement" is the predominant stage where you dream. And, the non-REM (NREM) sleep can be divided into non-REM phases one to three or four (depending on the type of categorisation you use).
The higher numbers of NREM sleep signify deeper sleep stages, such as NREM phases three and four.
For optimal sleep quality, it’s important to increase the amount of time you spend in the higher NREM phases as well as REM sleep. If you spend lots of time in NREM phrases one and two, you’re technically sleeping but the sleep is very non-restorative. Moreover, you need both the higher NREM phases as well as REM sleep for optimal sleep quality - missing either of them gives you suboptimal results.
So both REM sleep and the higher NREM sleep stages have different purposes. You need REM sleep for processing emotions as REM acts as a kind of nightly therapy, for heart and blood vessel health, creativity during the daytime, and optimising your learning ability (4; 5). The higher NREM sleep stages, moreover, are also necessary for learning and memory, as well as hormonal health and fat loss, immune function, and overall recovery of your nervous and musculoskeletal system.
So, both the higher NREM as well as REM sleep are important for sleep quality. So let's move to the topic of how saunas affect people differently next:
Will a Sauna Help Me Sleep Better?
So, before exploring whether a sauna before sleep is a good idea, let’s consider the concept of “biological individuality”.
Humans are not all the same. For instance, large variations exist between intelligence, strength, endurance, mental fortitude, and other measurable qualities. You can, for instance, have a very high IQ and very poor genetics for becoming a great basketball player - or the reverse. And, if you’re lucky, you have both a high IQ and great genetics to become a great basketball player, but, you will have a disadvantage in some gymnastic disciplines like the rings.
The same is true for both heat exposure whether that heat comes from infrared light or hot air (6; 7). Exposing yourself to infrared light increases heart rate, for instance, as well as your body temperature, but the extent differs from person to person.
Normally, during sleep, your body temperature goes down and becomes lowest during the middle of the night. The drop in body temperature already starts in the late afternoon though. If the drop in temperature is too significant, and you’re increasing your heart rate too much in the evening, your sleep quality will be negatively affected (8; 9).
The same is true for reaching an optimal body temperatures (10; 11; 12). Of course, very cold temperatures are bad for high sleep quality also, so a golden mean exists between too hot and too cold. In such a case, you'll spend less time in the REM phase of sleep as well as the higher NREM phases.
Now here’s where differences in heat tolerance explain the differences in sleep quality you might get from sauna sessions:
After spending 20 minutes in a traditional sauna, some people will have a heart rate of 120 beats per minute (13). Others will have a heart rate of 170 beats per minute - mathematically, that difference between these groups is only 2 standard deviations around the mean. Looking at the mathematical principle of the “Bell Curve”, 68% of people will have a heart rate between 120 beats per minute and 170 beats per minute.
Of course, the difference between 120 beats and 170 beats per minute is pretty big. Assuming a resting heart rate of 80, the increase in some study participants is twice as big as it is for others.
Regulation of heat can be partially trained by increasing aerobic conditioning, although other factors are beyond your control (13; 14; 15). For some reason, some individuals have a lower increase in heart rate and levels of stress hormones than others.
Differences in what are called “mitochondria” - the energy-producing factories of your cells - also result in the ability of cells to generate energy for movement versus heat production (16; 17; 18). In plain English, the makeup of your cells determines whether you’re better at withstanding cold temperatures or at physical exercise.
While more research is needed to explain why exactly there are individual differences between heat tolerance, right now, these differences do exist. And hence, you might respond to a sauna session differently than your good friend.
As a result, your heart rate or “heart rate variability” might recover less quickly than in another person. For that reason, some people don’t sleep better after the sauna.
Ferriss tracks his response to using an infrared sauna before sleep with a health and wellness tracker. The Oura Ring and Biostrap are examples that help you track your recovery and sleep. For Ferriss, his sleep quality goes down if he uses it right before bedtime. In plain English, Ferriss spends less time than is normal for him in the NREM phases 3 and 4, and in REM sleep,
However, to reap infrared sauna sleep benefits, Ferriss uses late afternoon and early evening sessions for superior results. That way, his stress response and heart rate can recover sufficiently so that sleep quality is positively instead of negatively affected.
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Foolproof Method to Ensure a Sauna Helps You Sleep
Even if you don’t have a health and wellness tracker like an Oura Ring or Biostrap EVO, you can still track how you’re doing.
For instance, you can measure your heart rate at your wrist with your index finger and get an indication if you’re recovering quickly or not. If your heart rate remains elevated just before bedtime, it’s probably best to plan your infrared sauna sessions earlier on the day.
But you don't necessarily need an Oura Ring or another device to measure whether you sleep well or not:
Instead, you can get a subjective indication of your sleep quality. For instance, having many dreams and intense ones is a sign your sleep quality is high. Waking up refreshed and without an alarm clock is also a sign you’re sleeping well. If you’re waking up groggy and don’t dream or remember any dreams, it’s an indication your sleep quality is poorer.
Measuring your resting heart rate in the morning is a great tool to measure recovery as well.
Then, there’s your ability to fall asleep after a sauna session. If you take longer than normal to fall asleep, you’ve planned your sauna session too close to bedtime. If you fall asleep better than normal, the timing is probably great for your biological individuality.
You might ask: “but what if the sauna makes me sleep a lot?” In that case, make sure to observe whether your sleep quality is high or not. If you’re sleeping better or equally well as normal, it’s probably great. If your sleep quality goes down and you’re sleeping a lot, you’re probably not recovering as well as you could.
By the way, red light therapy is very similar to the infrared sauna and sleep dynamic. Some people do great using red light therapy right before bed, while others are overly stimulated by it and need to use it in the late afternoon or early evening at the very latest.
Nevertheless, many studies show that people benefit from saunas for sleep on average - let's explore that dynamic now:
(Infrared) Sauna And Sleep Physiological Mechanisms
There are many different mechanisms through which sleep quality improves after a sauna session. Here are three of these mechanisms below, based on the latest science (19; 20; 21; 22; 23; 24).
Firstly, spending time in a sauna makes your body release natural opiates such as “endorphins” that make you feel very relaxed. Those endorphins are also responsible for the feel-good of a runner’s high and help you calm down before bed.
Secondly, after you spend time in a sauna the “parasympathetic” part of the nervous system is activated to a higher degree. That “parasympathetic” part has an emphasis on “rest and digest”, in other words, recovery, and ought to be more active when you’re trying to relax.
Thirdly and lastly, spending time in a sauna counters anxiety and improves the “serotonin” level in some people. Anxiety is a frequent cause of lower sleep quality and sleep deprivation for many because of a racing mind - serotonin is a brain-signalling compound that makes you feel that all is okay and well, in other words, comfortable. Comfort, in turn, helps sleep as well.
As a result of these three physiological mechanisms, sleep quality massively improves for many people after a sauna session. Below I’ve listed some outcomes from a Global Sauna Survey showing that these physiological mechanisms do indeed improve sleep quality:
A 1988 study with 1,600 participants in Finland found that sauna use was one of the most important strategies people commonly used for improving sleep quality. A 2019 study confirmed the viability of that strategy - 83.5% of study participants experienced sleep improvements after a sauna session (25; 26).
Most people thus have positive results, but if you’re among those who use a sauna and can’t sleep, you’ll have to use different timing. So, let's put that statement into perspective in the conclusion:
Using a Sauna and Can’t Sleep? Maybe it is Not For You
Everyone should be able to sleep better after the sauna. Sauna sessions have tons of benefits through different physiological mechanisms, such as activating the “rest and digest” part of your nervous system and increasing your serotonin production.
However, if you’re one of the individuals whose sleep responds poorly to late-night sauna sessions, you’ll have to plan your sauna sessions during the late afternoon or early evening.
That way, your heart rate can go down for the night and stress hormones have time to clear themselves from the system.
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