Sauna

Sauna bathing, sometimes referred to as (whole body) passive thermal or heat therapy is a simple and relaxing way to benefit from a fair number of potential health benefits such as reductions in cardiovascular & hypertension risks and oxidative stress.

Sauna bathing subjects the body to mild hyperthermia, where the core body temperature is raised to, or above 38°C/100.4°F, which is outside of the body's homeostatic range; it's state of optimal functioning, of which temperature is a one of many factors. Others include blood sugar levels, sodium and other mineral levels, hydration and blood pressure. This body temperature is considered high and is often called a fever when not caused by external conditions such as sauna use.

Don't let it concern you but direct cell death can occur at temperatures nearing 41°C/105.8°F. As you can imagine, your body's regulatory reaction to sauna bathing, designed to return you to homeostasis and maintain life, is fast and can be significant. Ensuring you are reasonably healthy, sober and well hydrated is essential to ensure your body is able to cope with the stresses involved.

It's this reaction that provides the benefits of sauna use. Your body's response involves, amongst other things; an increased heart rate and the production of sweat, heat shock proteins, pro-inflammatory cytokines and anti-inflammatory cytokines - the first three also occur during exercise.

Sounds fun right? Don't be put off, it's no different to exercise of nearly any kind; you subject your body to stress on a regular basis in order to stimulate an adaptive response. The adaptation could be stronger or bigger muscles, greater stamina, faster movement or all three. And as with exercise, you'll probably want a shower afterwards. Unlike exercise, little effort is involved other than tolerating the heat & sweating a great deal. You'll quickly become accustomed to it.

Benefits

There's little definitive evidence of the health benefits of sauna bathing and very little research had been published prior to the early 2000s. That said, a growing number of research papers, studies and reviews have been published since and these all suggest a very positive, albeit currently unproven, picture. Some of the possible health benefits of sauna bathing include;

increased blood flow and circulation to soft tissue, especially the skin
relaxed muscles
improved skin health
improved recovery and soreness after resistance training (infra-red sauna only) ¹⁸
drug-free bronchodilation (increased airflow to the lungs), including the loosening of mucus or phlegm (although this can be irritating for some)
promoting longevity (aka reducing all-cause mortality) ¹
reduced cardiovascular risk factors ¹
reduced blood pressure and reduced risk of hypertension ²
improved endothelial function ³ ⁴
reduced oxidative stress ⁵ ⁶
improved in cardiovascular function ⁷ ⁸ ⁹
reduced incidence of respiratory infections such as common colds, pneumonia and the severity of COVID-19 ¹⁴ ¹⁵ ¹⁶

Do keep in mind that most research has focussed on caucasian populations in Nordic countries as sauna availability and use is very high in them. Women are reasonably well represented in research. ¹⁰ ¹¹ ¹²

Myths

I've seen a lot of articles and sites claiming sauna use can result in detoxification of the body, particularly with regard to microplastics and so-called 'forever chemicals', such as PFAS. However, sweating only plays a minor role in detoxification; the liver, kidneys and digestive system are responsible for the majority of it.

There is no scientific evidence, nor any studies that prove or conclude otherwise.

Forms/Types

There are two common types of sauna, differentiated by their method of heating the body. In terms of potential health benefits, an infrared sauna is superior to a traditional Finnish sauna because you get all the benefits of sauna bathing, plus the additional benefits of all-body red light therapy.

Infrared (IR) Dry Sauna

A low heat (27-32°C/80-90°F maximum and usually considerably lower), low humidity (10-20%) environment generated using far-infrared (FIR) light waves to directly heat your body (rather than heating the air (convection), which then heats your skin and body (conduction)). This is far less intense and easier to tolerate than the higher heat of a traditional sauna and very similar to Waon therapy in Japan.

FIR Saunas are generally cheaper to run than a traditional sauna as the lower temperature requires less power. The infrared light/heat also penetrates deeper into soft tissue leading to increased sweating.

Far infrared light also has many additional potential health benefits. Typically called red light therapy, these include;

encouraging hair growth
reduced signs of skin ageing
reduced acute(1) and chronic(2) pain
promoting soft tissue repair and healing
reduced inflammation
improved cognitive function

rapid, severe, sudden, short term (broken bone, heart or asthma attack)
frequent, ongoing, long term, extended (osteoporosis, cancer)

Traditional Finnish Dry Sauna

A high heat (66-93°C/150-200°F), low humidity (10-20%) environment generated by either a wood burning stove or electric heater.

Wet Sauna

This can be either a traditional or infrared sauna (most often it's the former) but one that has a high humidity (60-100%) which makes it feel far hotter than it is. The high humidity typically fluctuates and requires some manual action by a sauna user to maintain, such as pouring water over hot stones.

It's easy to confuse a wet sauna with a steam room; while very, very similar, a steam room usually has a very constant 95-100% humidity and a medium heat of 43-49°C/110-120°F. Steam rooms also tend to be tiled rather than wooden for obvious reasons.

Compared to a dry sauna with low humidity, the moist air of a wet sauna or steam room may help soothe irritated nasal passages, loosen up phlegm and clear congestion, making it easier to breathe.

When to Avoid Use - Interactions/Contraindications

Sauna bathing subjects your body to stress so it's best to avoid it in some specific cases so you don't subject yourself to more stress than your body can handle, such as when you;

are pregnant (although it is very common for women to do so in Finland)
have low blood pressure (hypotension)
have consumed alcohol as this increases the risk of hypotension, arrhythmia and sudden death
are ill (a mild cough or cold is fine)
are dehydrated
have unstable angina pectoris
have experienced recent myocardial infarction
have severe aortic stenosis

Warning

If you have any significant, chronic medical conditions (particularly anything respiratory such as asthma, bronchitis or pneumonia), always consult a health professional before using a sauna.

If you are trying to conceive and male, be aware that sauna use reduces sperm count and motility and that it will take around 2 months for your sperm health to recover once you've stopped. Sauna use does not affect the fertility of healthy women.

Frequency, Timing & Duration

Any time of day is good but after exercise is a great time and may provide the benefits of a decrease in recovery time and soreness¹³.

You should aim to bathe for at least 20mins. If you are new to sauna bathing, I'd suggest starting at 5 minutes for at least two sessions and then increasing the duration by a further 5 minutes and so on for every two sessions until you reach your intended target duration. If your sauna has seats/benches at different heights, use the bottom seat/bench to start and once you've hit 20 minutes consider using the top seat/bench before you increase the session duration further.

To fully enjoy the long term benefits of sauna use, I'd recommend bathing at least three times a week.

Important

How often you bathe is more important than how long you bathe.

Bathing Protocol

have a drink of water before you enter
consider where you sit in a traditional sauna (and even an infrared to a lesser extent); the higher you go, the hotter it will get
if you get dizzy, light headed, nauseous or sick end your session immediately
have a drink of water afterwards - consider an electrolyte drink if you've sweated a considerable amount and/or have bathed for over 30 minutes (a piece of fruit and something salty will also suffice)

Fitness Trackers

Beware, fitness trackers will record your heart rate just fine, but may mistake your bathing session for exercise because they make the mistaken assumption that your increased heart rate is related to activity. As an example, we recently did a 20 minutes session in a traditional sauna and my tracker recorded a peak heart rate of 151bpm, 49 zone minutes, a calorie burn of 346 and logged the session as 'intense activity'.

Further Information

Infrared Wavelengths

The term infrared light encompasses a number of wavelengths, each with different properties. The ISO 20473 scheme¹⁷ classifies the wavelength ranges as follows;

Designation	Abbreviation	Wavelength	Uses
Near-infrared	NIR	0.78–3μm/780-3k nm	Skin, hair
Mid-infrared	MIR	3–50μm/3k-50k nm
Far-infrared	FIR	50–1,000μm/50k-1m nm	Sauna