If you have ever left a sauna or steam room feeling calmer than when you went in, you may have wondered what changed. The warmth, the quiet and the chance to stop for a while can all be part of the experience. Heat also produces measurable changes in your body, including its hormonal response.
That makes the science interesting, but it does not give us a simple formula for feeling good. Some responses are well documented; their contribution to mood, sleep and longer-term brain health is less certain.
What Happens When Your Body Heats Up?
In a sauna or steam room, your body works to keep its temperature under control. Blood vessels near the skin widen, heart rate rises and you sweat to lose heat. How demanding this becomes depends on the temperature, humidity, time spent inside and your own health and familiarity with heat.
Traditional saunas commonly operate at around 70-90°C, while steam rooms use lower temperatures and very high humidity. Infrared saunas generally operate at lower air temperatures too, heating the body differently. These are distinct experiences, and findings from one should not automatically be applied to the others.
Some cardiovascular responses resemble those seen during exercise, but sitting in the heat is not equivalent to exercising. Nor does a higher heart rate tell us that a session is producing a particular brain-health benefit.
What Does the Research Say About Hormones?
Studies of traditional sauna bathing have measured changes in several hormones and chemical messengers. The results depend on the conditions, and some experiments used much more intense heat than a comfortable everyday session.
- Beta-endorphin: Some studies have found increases in this substance, which is involved in the body's response to pain and stress. However, a rise in the blood does not directly tell us what is happening in the brain or prove that it causes post-sauna pleasure.
- Noradrenaline: Also called norepinephrine, this can rise during heat exposure as part of the body's response to physical stress. It should not be interpreted as evidence that a sauna improves concentration or produces alertness without anxiety.
- Prolactin and growth hormone: Increases have been recorded under certain sauna conditions. These are physiological findings, rather than proof of better mood, faster recovery or improved brain function.
- Cortisol: The response is variable. Studies have reported different results depending on the heat exposure and when measurements were taken. Feeling relaxed afterwards does not necessarily mean your cortisol has fallen.
For example, one small Finnish sauna study involved eight young men exposed to different conditions until discomfort or exhaustion. It demonstrated hormonal responses to heat, but it was not a test of whether a gentle sauna session makes people happier. It is certainly not a routine to copy.
Why Can a Session Feel So Relaxing?
Hormones may contribute, but they are unlikely to explain the whole experience. Warmth can feel comforting, and a sauna or steam room gives you somewhere to sit without a phone, a task to finish or another demand on your attention.
For some people, that pause is the most noticeable benefit. Others enjoy the company, the quiet or the feeling of cooling down afterwards. These experiences matter even when we cannot attribute them to a particular chemical change.
If you regularly feel better after a comfortable session, that is a useful personal observation. It does not need to become a claim that heat resets the nervous system or treats a mental health condition. We explore this further in our article on sauna and steam for mental wellbeing.
Can Heat Help You Sleep?
There is a plausible connection between warming up, cooling down and preparing for sleep. Your core temperature normally falls as bedtime approaches, and losing heat through the skin is part of that process.
A systematic review found that warm baths or showers taken around one to two hours before bed could help people fall asleep more quickly and improve some measures of sleep quality. That research concerned water-based heating, so it does not establish the same effect or an ideal schedule for sauna and steam room use.
An evening session may still be a pleasant way to wind down. Leave enough time to cool comfortably before bed and notice how you respond. If you feel overheated or more alert afterwards, an earlier session may suit you better. There is no need to force a routine that makes sleep harder.
BDNF: Does Heat Support Learning and Memory?
Brain-derived neurotrophic factor, usually shortened to BDNF, is a protein involved in nerve-cell survival and the connections that support learning and memory. It is one reason researchers are interested in the possible effects of heat on brain health.
Small human studies have found increases in circulating BDNF after certain forms of heating. One involved eight healthy men immersed up to the neck in hot water. A separate trial found increased blood BDNF after a ten-week programme of repeated, controlled heat exposure.
Those findings are worth investigating, but measuring BDNF in the blood is not the same as measuring an improvement in memory or learning. BDNF also comes from tissues outside the brain, and the studies do not establish that an ordinary sauna or steam room session improves neuroplasticity.
For now, it is an interesting research question. It is not a reason to stay in longer, turn up the temperature or try to reproduce laboratory heat exposure at home.
Sauna or Steam: Is One Better for the Brain?
There is not enough direct comparative evidence to say that one is better for mood, sleep or brain function. Much of the hormonal research concerns traditional Finnish sauna bathing, while some BDNF studies use hot water or specialist heating equipment. Steam rooms and infrared saunas cannot simply inherit those findings.
Humidity does make a practical difference. Sweat evaporates more readily in dry air, helping the body lose heat. In a steam room, high humidity limits evaporation, so a lower air temperature can still feel demanding.
Choose the experience you enjoy and can use comfortably. Neither needs to feel intense to give you a worthwhile break, and feeling hotter is not evidence of a greater benefit.
Using Heat Comfortably and Safely
Research protocols are designed for supervised experiments, not as targets for everyday use. Follow the guidance for the facility or equipment, and leave before you feel you need to endure the heat.
- Keep your first sessions brief: Take time to discover how you respond. You do not need repeated rounds or a set number of minutes to make a session worthwhile.
- Drink water: Arrive hydrated and replace fluids afterwards. For an ordinary short session, there is no need to routinely add salt to your drink.
- Cool down gradually: Give yourself time to recover and stand up slowly. An abrupt cold plunge is optional and introduces its own physical demands.
- Avoid alcohol: Do not use a sauna or steam room after drinking, or when you are already dehydrated or unwell.
- Leave if you feel unwell: Dizziness, nausea, headache or weakness are reasons to stop and cool down. Get medical advice if symptoms persist. Chest pain, severe breathing difficulty or collapse require urgent help; call 999 in an emergency.
- Check whether heat is suitable for you: Speak with your clinician if you have a heart condition, recurrent fainting, difficulty regulating body temperature, or take medicines that affect sweating, hydration or blood pressure. If you are pregnant, discuss sauna and steam room use with your maternity team because of overheating and fainting risks.
What This Means for Everyday Use
A sauna or steam room can be an enjoyable place to slow down, and heat does produce measurable physiological changes. The evidence is less clear about how those changes explain relaxation or translate into lasting benefits for the brain.
You can enjoy the calm without chasing a hormone response. A comfortable session that fits your life is a more useful starting point than trying to achieve a particular temperature, duration or laboratory result.
Sources and Further Reading
- Kukkonen-Harjula et al. (1989). Haemodynamic and hormonal responses to heat exposure in a Finnish sauna bath. A small experimental study illustrating how responses vary with heat conditions.
- Endocrine effects of sauna bath. An overview of hormonal findings, including the variable cortisol response.
- Haghayegh et al. (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep. A systematic review and meta-analysis of water-based heating, rather than sauna or steam rooms.
- Kojima et al. Head-out immersion in hot water increases serum BDNF in healthy males. A small study measuring blood BDNF after hot water immersion.
- Glazachev et al. (2020). Repeated hyperthermia exposure increases circulating BDNF levels. A randomised trial of a controlled ten-week heat programme.
- Serum and plasma BDNF concentration are elevated by systemic but not local passive heating. Further experimental research into circulating BDNF.
- NHS: Heat exhaustion and heatstroke. Symptoms, cooling advice and when to seek help.
This article provides general information. Sauna and steam room use should not replace medical assessment or treatment for persistent sleep, mood or other health concerns.
