From Heat to Rest: How the Sauna Promotes Deeper, More Restorative Sleep

Introduction: Sauna nights and deep sleep

Saunas have long been a pillar of Nordic wellness culture, especially in Finland and Sweden. Many Europeans enjoy the evening ritual of löyly (sauna steam) not only to relax, but also for its sleep benefits. Interestingly, Finns often say that a sauna before bed helps them get a deep sleep, and now science is proving it. Recent research - much of it Nordic - is revealing proven links between sauna use and improved sleep quality. From physiological effects on body temperature and stress hormones to impacts on sleep stages such as REM and deep sleep, sauna bathing seems to prepare our bodies for better rest. This article explores the science of sauna and sleep, based on findings from Finland, Sweden and other countries, and offers practical guidance for European homeowners who want to use the sauna as a tool for healthier sleep.

Saunas and sleep: what research shows

Numerous studies have shown that saunas can improve sleep quality. In Finland, where saunas are ubiquitous, people have long ranked sauna sessions among the best aids to a good night's sleep. In a large Finnish survey of 1600 middle-aged adults, the sauna (along with showers and baths) was frequently cited as a positive influence on sleep. More recently, a global sauna survey carried out in 2019 by researchers in Australia found that 83.5% of regular sauna users reported sleep benefits after sauna use (Hussain et al., 2019). These self-reported benefits range from falling asleep more quickly to having a deeper, more restorative sleep.

It is important to note that controlled studies confirm these subjective reports. The only experiment dedicated to directly monitoring the impact of the sauna on sleep architecture was carried out in Finland in the 1970s. In this small study, five volunteers had their sleep monitored after an evening sauna compared to a night without a sauna. The results were impressive: the sauna bath increased the amount of deep slow-wave sleep by more than 70% in the first two hours of the night (and by around 45% in the first six hours) compared to the night without a sauna, while the time spent awake during the night decreased significantly (Putkonen & Elomaa, 1976). The sauna night also led to an easier start to sleep for most of the participants. These findings, although from a small sample, gave initial scientific confirmation to what sauna enthusiasts intuitively felt: a sauna before bed can lead to a noticeably deeper sleep.

Modern data echoes these findings. Wearable sleep monitoring devices are providing large-scale evidence of the effects of the sauna on sleep stages. For example, analysis of data from users of the Oura Ring (a popular Finnish sleep monitoring device) showed that on nights after sauna use, people had, on average, around 15% more deep sleep and 11% more REM sleep than on nights without a sauna. Total sleep duration and heart rate variability (a marker of relaxation) also improved. Although these data are observational, they are in line with controlled findings that sauna use preferentially increases the more restorative phases of sleep (deep sleep) and can even modestly increase REM sleep - an important phase for memory and mood.

In addition to Finland, the connection between sauna habits and sleep quality has been observed in Sweden. A 2024 population study in northern Sweden (part of the MONICA health survey) compared more than 600 sauna users with those who never use saunas. The sauna users "reported higher levels of happiness and energy, more satisfactory sleep patterns, as well as better general and mental health" than the non-users (Engström et al., 2024). Notably, this study found that it may not be necessary to do daily sessions to reap the benefits - participants who attended the sauna only 1 to 4 times a month reported the best well-being and sleep, while those who attended more frequently (2 to 7 times a week) showed no additional improvements. In other words, a moderate sauna frequency was enough to sleep better and feel healthier, at least in this Swedish cohort. (This contrasts somewhat with previous Finnish guidelines, which suggested sauna almost daily for maximum health benefits, but it's encouraging that even weekly sauna nights can help).

Taken together, the evidence suggests a strong link between sauna bathing and better sleep. But how does sitting in a warm wooden room translate into better sleep? The answer lies in the way saunas influence our body's thermoregulation, circadian biology, stress response and even brain chemistry - all essential components for healthy sleep. Let's take a closer look at the mechanisms.

Warming up to relax: thermoregulation and circadian rhythm

One of the main ways in which a sauna session can promote sleep is through its effects on regulating body temperature. Normally, our body's core temperature follows a daily circadian cycle: it peaks in the late afternoon or early evening and then drops at night to help initiate sleep. In fact, a slight decrease in core body temperature at night - around 0.5 °C to 1 °C - is a natural signal that facilitates the onset of sleep (Haghayegh et al., 2019). During the night, core temperature remains low and then begins to rise at dawn as a signal to wake up. This close link between temperature and the sleep-wake cycle means that manipulating body heat before bed can influence how easily you fall asleep and the type of sleep you get.

Sauna bathing provides a form of passive body heating that can be strategically programmed to take advantage of this physiology. When you sit in a hot sauna, your core body temperature can rise by up to 1-2 °C (for example, in a Finnish study, 30 minutes in the sauna increased the core temperature by around 2 °C). You will leave the sauna feeling very hot and flushed. Then something interesting happens: as you cool down, vasodilation (widening of the blood vessels) in your skin continues, releasing heat from your core into the environment. This post-sauna cooling phase can accelerate the normal drop in body temperature during the night. Essentially, the sauna triggers your body's cooling mechanisms, so that around 60 to 120 minutes later, your core temperature drops to a lower range, which signals to your brain that it's time to sleep.

Research has shown that this effect significantly improves the onset and quality of sleep. In studies with people suffering from insomnia - especially the elderly - increasing body temperature by approximately 1 °C about 1 to 2 hours before bedtime led to significantly faster sleep onset (people fell asleep about 36% faster) and longer deep slow-wave sleep during the night (increase of about 10%) (Dorsey et al., 1996). Although these studies used hot baths as the heating method, the principle is the same for the sauna: after exposure to heat, the body cools down and this cooling "signals the hypothalamus to trigger sleepiness". A 2019 systematic review of 17 trials also concluded that passive heat therapy before bed reliably reduces sleep onset latency and improves overall sleep efficiency, especially when done about 90 minutes before lights out (Haghayegh et al., 2019).

In simple terms: if you heat up, you'll cool down more later - and that cooling down makes you sleepy. Scheduling a sauna session in the evening (more on the ideal time later) helps your body enter the cooling phase at the right time for sleep. This takes advantage of your natural circadian rhythm, essentially giving your internal clock a nudge in the direction of sleep.

It's also worth noting that as the core temperature drops, the body increases its production of melatonin, the hormone that signals darkness and sleep. The increase in melatonin usually coincides with a drop in temperature at night. By using the sauna to induce an earlier or stronger decline in temperature, you can also stimulate an earlier release of melatonin (University of Eastern Finland, 2018). Some emerging evidence even suggests that the type of light in certain infrared saunas (which often emit infrared/red light) can increase melatonin levels. Near-infrared wavelengths can penetrate tissues and have been found to trigger extra-pineal melatonin synthesis in cells. In a pilot study, a 45-minute full-spectrum infrared sauna session increased salivary melatonin by around 64% at bedtime, potentially aiding sleep onset. Traditional Finnish saunas, taken in dim light or by candlelight, also avoid exposure to blue light and therefore do not suppress melatonin in the way that screen time would. The main conclusion: through thermal and possibly light-related pathways, an evening sauna can help align the body's circadian signals (temperature and hormones) with the goal of falling asleep.

Stress relief and hormonal balance for better sleep

In addition to the temperature effects, sauna bathing powerfully engages the autonomic nervous system and the endocrine (hormonal) system, which can translate into a calmer mind and body at bedtime. A sauna session is often described as deeply relaxing - and there's a physiological truth to that. The intense heat causes your heart rate to increase and your circulation to speed up, mimicking moderate exercise. This is a form of positive stress (a hormetic stress factor), and the body responds by activating the parasympathetic "rest and digest" system to regain balance.

An immediate effect after the sauna is a pleasant feeling of calm. Studies using questionnaires and even neuroimaging have observed a reduction in anxiety and a shift to the parasympathetic domain after sauna use. For example, in the Swedish MONICA survey, regular sauna users had significantly lower levels of self-rated anxiety and stress and reported feeling more relaxed than non-users (Hägglund et al., 2024). This relaxation response is vital for sleep: a calmer nervous system helps not only to fall asleep faster, but also to stay asleep without disturbing awakenings caused by stress or rumination.

Behind the scenes, the heat of the sauna triggers the release of various hormones. Notably, cortisol, the main stress hormone, initially increases during sauna exposure (as part of the body's response to heat stress). However, with regular sauna practice, baseline cortisol levels can actually decrease. Finnish researchers found that after repeated sauna sessions (daily for a week), participants' resting serum cortisol levels dropped significantly by the end of the week (Leppäluoto et al., 1986). In other words, taking regular sauna baths can attenuate your overall level of stress hormones, potentially making you less prone to the nocturnal cortisol spikes that interfere with sleep. High cortisol at night is a known culprit for insomnia - it opposes melatonin and keeps the brain alert. So a habit that reduces cortisol (or helps to dissipate it after acute heat stress) is very conducive to better sleep.

Sauna use also affects other hormones and neurotransmitters linked to mood and sleep. Endorphins (peptides that provide well-being and pain relief) increase during sauna bathing, contributing to post-sauna euphoria and muscle relaxation. Some research suggests that sauna bathing can also increase serotonin, or at least the availability of its precursor, tryptophan (serotonin is a precursor of melatonin and promotes relaxation). As observed by sleep scientist Markku Partinen, the increase in body temperature in the sauna increases serotonin metabolism and reduces noradrenaline levels in the brain, which correlates with decreased alertness and an easier transition into deep sleep. This biochemical change - more serotonin and less noradrenaline - creates a brain state conducive to sleep: calm, content and less vigilant.

In addition, regular sauna practice can improve heart rate variability (HRV), an indicator of the balance of autonomic function. Higher HRV (especially during sleep) generally reflects better recovery and resilience to stress. One analysis found that when individuals had a 20-minute infrared sauna session before bed, their nocturnal HRV (RMSSD values) was 10-15% higher on average, indicating a stronger parasympathetic (relaxation) response during sleep. Although more research is needed, these findings are in line with the notion that sauna use helps to "switch off" the body's fight or flight mode and activate the rest and recuperation mode - exactly what is desired at night.

In short, sauna bathing helps reduce the physiological barriers to good sleep. By decreasing stress hormones such as cortisol, increasing relaxation chemicals and relieving muscle tension and pain (which also improves sleep comfort), a sauna session sets the stage for a more restful night. It's a holistic relaxation ritual that calms the mind and body. As reported by the Global Sauna Survey, among people with certain medical problems, such as chronic pain or depression, many cited sauna sessions as a significant improvement in their condition and sleep - probably due to this potent stress-relieving and mood-enhancing effect.

Sauna and sleep architecture (deep sleep vs. REM sleep)

The quality of sleep is just as important as the quantity. Researchers usually assess the quality of sleep by looking at its architecture - the cycle between light sleep, deep sleep and REM (dream) sleep. The aim is to spend enough time in both deep sleep (also called slow-wave sleep, stages 3-4) and REM sleep, as these stages are essential for physical restoration, memory consolidation and emotional processing. Sauna use seems to influence this sleep architecture in beneficial ways.

As mentioned, the Finnish study by Putkonen & Elomaa observed a dramatic increase in deep sleep after the sauna. Deep sleep in the first part of the night is when body restoration and cell repair are most intense and growth hormone is released. The extent of sauna-induced deep sleep (70% more in the first 2 hours) suggests that heat stress and subsequent cooling can intensify the depth of your sleep cycles. The participants also had fewer awakenings during the night after the sauna, indicating more continuous sleep. This is in line with many reports from sauna users that they "sleep like a rock" after a good sauna - not just falling asleep quickly, but staying asleep for longer.

What about REM sleep? Early studies didn't observe a big change in REM duration on sauna nights, but more recent data from wearable devices suggests that REM sleep can also increase modestly. Data from the Oura Ring, for example, showed an average 11% increase in REM time on sauna nights compared to non-sauna nights. Although 11% may not seem like much, over time this can significantly improve cognitive and emotional health, as REM is vital for memory consolidation and mood regulation. One reason the sauna can help with REM sleep is that it improves overall sleep continuity - when you don't wake up as often, your REM cycles (which occur mainly in the last hours of the night) remain uninterrupted and can extend naturally. In addition, the anxiety-reducing effects of the sauna (lower cortisol and adrenaline) probably prevent stressful dreams or shallow REM.

Another aspect is that, by increasing the time of deep sleep initially, the sauna can gently compress the lighter stages of sleep, effectively reorganizing the nightly cycles towards more restorative phases. Some studies on sleep with passive heating observe an interesting phenomenon: a hot bath before bed can slightly delay the circadian phase of core body temperature and sleep in older insomniacs - essentially pushing sleep architecture to more closely resemble that of younger adults with more slow-wave sleep (Dorsey et al., 1996). In other words, heat therapy can counteract the age-related decline in deep sleep. This is especially promising for middle-aged and elderly sauna users who wish to maintain a youthful, healthy sleep.

It's also worth mentioning muscle relaxation and pain relief - although they are not a "sleep phase", they indirectly affect sleep architecture by reducing awakenings. The heat from the sauna penetrates the tissues, increasing blood flow and helping to relax tense muscles. The Finnish sauna tradition often includes gentle stretching or the use of a birch whip to massage the muscles, further relieving tension. Less muscle tension and joint pain means fewer pain-related awakenings during the night and more time in deep/REM sleep. In fact, clinical trials have found that chronic pain patients who use saunas regularly report reduced pain and improved sleep (a Japanese study on fibromyalgia showed significant pain relief and better sleep after 3 weeks of daily sauna therapy). The reduction in pain allows the body to plunge into deeper sleep phases without interruption.

Conclusion: saunas can improve the quality of your sleep, not just knock you out. By promoting a healthy balance of sleep stages - increasing deep sleep, potentially aiding REM and minimizing middle-of-the-night awakenings - sauna bathing contributes to more invigorating sleep. Over time, this can improve daytime energy, cognitive function and general well-being. As one Swedish researcher put it: "What makes us sleep better [after the sauna]? We want to understand the root causes" - current evidence points to a combination of thermoregulatory and stress-relieving changes that are ultimately reflected in our sleep architecture.

Traditional sauna vs. infrared sauna: does it matter for sleep?

Today, homeowners can choose between traditional Finnish saunas (electric or wood-fired heaters that heat the air, often used with water vapor on stones) and infrared saunas (heating elements that emit infrared radiation to directly heat the body at lower temperatures). Both types can help with sleep, but there are some differences in the experience and, potentially, the effects:

• Temperature and tolerance: Traditional saunas operate at high temperatures - usually 70 °C to 90 °C (sometimes up to ~100 °C) - with low humidity (or higher humidity if water is added for steam). Infrared (IR) saunas operate at lower temperatures, usually 45 °C to 60 °C air temperature. For sleep purposes, the gentler heat of IR saunas can be advantageous for those who find extreme heat too stimulating, especially around bedtime. The body still heats up (the IR rays penetrate the skin ~3-5 cm to heat the muscles and blood), but the ambient thermal stress is less intense. This means that infrared sessions can be longer and more relaxing for heat-sensitive people, while users of traditional saunas can only tolerate 10-15 minutes at 90 °C before they need a break to cool off. If you're the type who gets overly energized by too much heat, an infrared sauna in the evening can be more relaxing and make you less "excited" before bed.
  

 

• Humidity and breathing: Traditional saunas, especially when they use steam (löyly), create a moist heat that some people find very relaxing for the respiratory tract - similar to the effect of a steam room. This can help clear the sinuses and can benefit those whose sleep is disturbed by congestion. Infrared saunas are a dry heat, with no additional humidity. Both can relax the airways, but the moist heat of a Finnish sauna can be even more soothing for some people (although this also means that you will sweat more profusely in a shorter period of time).
  

 

• Melatonin and exposure to light: As noted above, infrared saunas generally emit wavelengths of infrared and red light. Research in photobiology suggests that these wavelengths can stimulate melatonin production in cells and have a positive effect on melatonin production. phototherapeutic benefits. Traditional saunas are generally poorly lit (often with warm-colored lights or candles), which is good for not suppressing melatonin, but they don't actively emit light that affects cells. Although the melatonin-boosting claims of infrared saunas need further study, some experts propose that, if there is some extra increase in melatonin, infrared may have a slight advantage for sleep. For example, the Oura Health team observed that "if you're using a sauna to sleep, infrared can offer a more effective slight advantage in the form of an additional increase in melatonin" (Oura, 2023). However, it's important to keep this in perspective - both types of sauna primarily aid sleep through thermal mechanisms and relaxation, and bright lights should generally be avoided in the hour before bedtime, whether you're in the sauna or not. So if you have a chromotherapy feature in an IR sauna, use soothing red tones at night, not blue lights.
  

 

• Cardiovascular load: Traditional saunas at ~90 °C induce a stronger cardiovascular response (changes in heart rate and blood pressure) similar to vigorous exercise, while IR saunas, at ~55 °C, produce a milder cardiovascular load (more like brisk walking). For most healthy people, either is suitable and can even improve cardiovascular fitness. But if someone is older or has a heart condition and wants to use the sauna specifically to help them sleep, the gentler heat of the infrared sauna may be safer or more comfortable - always consult a doctor in such cases. From a sleep point of view, the secret is how you feel afterwardsThe ideal is to feel pleasantly tired and relaxed, not dizzy or exhausted. Some people achieve this with a short traditional sauna; others prefer the longer, less intense heat of infrared.
  

In short, both traditional and infrared saunas can be effective sleep aids. They just achieve the effect with slightly different profiles. The traditional Finnish sauna offers the authentic experience of intense heat that many love - and certainly provides the benefits of cooling down after the heat - but may require more careful timing (to ensure complete cooling before bed). The infrared sauna offers a modern twist: a gentler heat that you can stay in for longer, which can be easier to incorporate at the end of the day and can confer some additional light-based benefits. However, research comparing the two for sleep is still limited. It probably comes down to personal preference and how your body responds. As one wellness expert put it, the best sauna is the one you use consistently - so choose the one that makes you feel good and fits in with your routine.

Tips for using the sauna to improve your sleep

If you're ready to turn your sauna into a tool for improving sleep, keep these practical guidelines in mind. These tips are based on research findings on thermotherapy for sleep and proven Nordic sauna habits:

• Timing is everything: use the sauna to in the evening, about 1 to 2 hours before bedtime. This allows the core body temperature to increase and then decrease in sync with natural circadian cooling. Many experts recommend starting the sauna around 90 minutes before going to bed. For example, if the lights go out at 10:30pm, start the sauna at around 9pm. This time optimizes the drop in body temperature after the sauna and the release of melatonin, so that you feel sleepy at the right time. Avoid an intense sauna session very close of bedtime (within 30 minutes) - you may feel excessively hot or stimulated when you should be falling asleep.
  

 

• Set the temperature to relaxing: For a traditional Finnish saunaan air temperature of 70-80 °C is sufficient to obtain sleep benefits - you don't need to turn up the heat to the maximum. In fact, extremely high temperatures (90 °C+) late at night can be over-stimulating or dehydrating. For infrared saunas, try to achieve 50-60 °C (if you're a beginner, start at around 45 °C). In an infrared cabin, 60-65 °C is often the upper limit for experienced users and provides deep heat without the air being suffocating. Remember that the goal is to relax the body, not to see how extreme a temperature it can withstand. Moderate, comfortable heat will still raise your body temperature by a degree or more if you have enough time.
  

 

• Session duration: When you start, keep the sessions moderate - about 15 minutes in the sauna and then see how you feel. You can gradually increase to 20 to 30 minutes per sessionas tolerated. Research into sleep improvements has used protocols ranging from a quick 10-minute hot bath to a 30-minute sauna. Most sauna-goers consider that 15 to 20 minutes in a traditional hot sauna or 25 to 30 minutes in a softer infrared sauna are the ideal spot for relaxation. It's perfectly acceptable to do a few shorter sessions (for example, two 10-minute sessions separated by a cold shower) if that's more comfortable - just finish the last session at least half an hour before bed.
  

 

• Frequency: consistency helps. Try to do sauna sessions at least 2 to 3 times a week to get continuous sleep benefits. You don't necessarily have to sauna every night (and, as the Swedish study suggested, even a few times a month has already shown benefits). However, many people incorporate it into their evening relaxation routine. If you like it and feel it helps, evening sauna sessions are great - just make sure you stay hydrated and listen to your body. There seems to be no harm in doing it daily for healthy individuals, but even a regular schedule like Monday, Wednesday and Friday evenings can significantly improve sleep consistency.
  

 

• Moisturizing and cooling: Always replenish your fluids after sweating in the sauna - a glass of water or an electrolyte drink will prevent dehydration which could otherwise disturb your sleep (waking up thirsty or with a headache). Also, take a warm or cold shower after the sauna. This helps to rinse away the sweat and starts the cooling process. In Finland, it's common to take a cold shower or even a quick dip in cold water; the contrast can relax you even more, but it's optional. Even just sitting in a cool room after the sauna for 15 minutes, perhaps with a soothing herbal tea, can be part of your pre-sleep ritual. Make sure your body stopped sweating actively and cooled down before going to bed - you'll sleep more comfortably.
  

 

• Create a relaxing atmosphere: use the time in the sauna to disconnect and de-stress. Consider soft lighting (or no light at all), silent meditation, soft music or simply conscious breathing while sweating. Avoid bright screens or work discussions in the sauna. That way, when you're done, your mind will be as relaxed as your body. Some people incorporate aromatherapy (such as a drop of eucalyptus or lavender oil in the steam water) to increase relaxation - just use the scents sparingly and safely. A relaxed state of mind will make it easier to fall asleep when you're in bed.
  

 

• Get to know your body: Finally, pay attention to how your individual body responds. The goal is to feel pleasant sleepy, not exhausted. If you find that a very long or extremely hot session leaves you very exhausted or speeds up your heart rate in the evening, reduce the intensity or duration next time. Similarly, if you feel you're not warmed up enough afterwards (unlikely, but let's say a low-temperature infrared sauna didn't raise your body temperature much), you can extend it a little longer or increase the temperature. Everyone's thermal tolerance is different. By experimenting within safe limits, you'll discover the sauna routine that lets you calm, sleepy and ready for bed.
  

Conclusion: Adopting the sauna sleep ritual

There's a reason why the sauna bath is often called the "sleeping pill" in Finland. As we've seen, science proves what sauna lovers have always known: a good sweat session at night can pave the way for deeper, better quality sleep. By affecting thermoregulation, circadian signals, stress hormones and even the time we spend in REM and deep sleep, regular sauna use can help reset our sleep patterns onto a healthier footing. It's an ancient wellness practice perfectly suited to modern life, where stress and insomnia often go hand in hand.

For European homeowners who invest in a sauna for health and relaxation, improved sleep may be the most appreciated benefit of all. Imagine ending your day with a soothing hot bath, stepping out into a cool breeze (or a cold shower) and then lying in bed as your body temperature drops and your eyelids feel heavy. When you turn off the lights, your muscles will be relaxed, your mind will be quiet and you can literally feel sleep enveloping you. Over time, this can translate into better productivity, mood and overall vitality thanks to a good night's sleep.

If you're ready to experience the scientific sleep benefits of the sauna, consider making it a consistent part of your evening routine. Your body and mind will thank you when you wake up refreshed. And if you don't already have a sauna at home, maybe it's time to create your own nighttime sanctuary of warmth and calm - the best remedy for restful sleep. Sweet dreams (and sauna steam)!

(P.S. Looking for the perfect home sauna? Explore our selection of luxury Finnish and infrared saunas here to start your journey to better sleep and well-being). 😊