Regular sauna use has been shown to do everything from improving sports performance to increasing the number of mitochondria in your cells, to improving immune function, to reducing the incidence of Alzheimer’s, and much more.

1. Combats Aging and May Increase Longevity
We can start by looking at the benefit of sauna use on longevity since this is the big picture. If a therapy reduces death from all causes, you can be sure that there are multiple mechanisms at work that are enabling this to happen (many of which we will get into in more detail below).
So does using a sauna actually impact on how long we live?
A study out of Finland followed 2,315 men (aged 42-60) for 20 years (studies this long are very rare) and found that those using the sauna 2-3 times per week (as opposed to just one time per week) were a whopping 24% less likely to die from all causes. But there’s even more – the effects continued to increase the more one used the sauna. Those using the sauna 4-7 times per week were an amazing 40% less likely to die from all causes.
One of the mechanisms for this may be the activation of heat shock proteins (HSPs). Aging is associated with a progressive accumulation of molecular damage and reduced cellular defense mechanisms.[3] HSPs can repair damaged cells, promote autophagy (the recycling of damaged cell parts) and also prevent future damage by scavenging free radicals and increasing antioxidant capacity through the maintenance of glutathione, a master antioxidant.
Higher levels of HSPs have been linked to longevity, as women with a gene polymorphism that leads to increased expression of HSPs live longer.

2. Mitochondrial Health and Energy Production
Heat stress is a powerful type of hormesis, and heat shock proteins (that special type of proteins that are strongly elevated in response to heat exposure) play a big role in improving mitochondrial health and function.
Why is that important?
Simple: Mitochondria are the energy generators in our cells, and our energy/vitality depend directly on their size, power, number, and function.
If your mitochondria are damaged, weak, small, fragile, and unhealthy, then you will be too.
Moreover, a huge body of emerging research is now pointing to mitochondrial health/function as a major root cause of dozens of chronic diseases and even aging itself.
While there are only a few studies testing this directly, heat stress has been shown to induce profound changes in mitochondrial health.
Heat stress (e.g. using a sauna) likely improves mitochondrial health in a number of ways:
Mitochondrial biogenesis – stimulates the body to make more mitochondria, which means greater capacity to produce energy
Mitochondrial growth – makes bigger, stronger mitochondria that produce more energy
Improvements in the Antioxidant Response Element (A.R.E.), the internal anti-oxidant and detoxification system.
Autophagy and mitophagy – stimulates the cells to recycle and repair damaged mitochondria (think of it like housekeeping and taking the garbage out)  

3. Enhances Detoxification
Saunas may also be the single most powerful tool we have for detoxification from environmental chemicals and heavy metals. Sauna use shows real promise for detoxification from heavy metals, PCBs, PBBs, BPA, drugs, and organochlorine pesticides such as DDT (which has been banned for decades but is still ubiquitous).
Many toxicants have long half-lives and bioaccumulate up the food chain, so even if you are avoiding new exposures to the extent possible by cleaning up your immediate environment and being careful about household and personal care products, no one can avoid all exposures and most people likely already have significant stores of toxicants. In our current world, even newborn babies have already been exposed, as a total of 287 toxic chemicals were identified in umbilical cords in a recent study.
How Saunas Help Your Body’s Detoxification Process
The ability to sweat seems to be critical for detoxification, and some toxicants, such as certain heavy metals, appear to come out in higher concentrations in sweat than via other excretion pathways such as urine or feces.   Think about that – when you sweat, you are literally pumping metals like mercury, cadmium, arsenic, and lead out of your body!
Studies have found that we sweat out everything from mercury, to BPA (a hormone-disrupting chemical from plastics), to PCBs, to DDT, to prescription drug residues, to fluoride, to countless other harmful chemicals. Sweating appears to be a major detoxification pathway in humans. And this is extremely problematic because many humans in the modern world don’t live the outdoor, physically active lifestyles of our ancestors (where ample daily sweating was the norm), and thus many modern humans rarely or almost never sweat to a significant degree. So we live in a far more toxic world than our ancestors, and we simultaneously stimulate our sweating detoxification pathway far less than they did – a bad combination indeed.
People with high levels of toxicants often have autonomic dysfunction that affects thermoregulatory mechanisms.  Sauna improves autonomic function and consequently thermoregulatory mechanisms, increasing the ability to sweat. People who are heat-acclimated through sauna use can produce up to 2 liters per hour of sweat.  The point is that accumulating toxins in your body can literally make it harder for your body to get rid of toxins – creating a vicious cycle. Sauna use helps break that cycle and helps your body re-learn how to detoxify.
Toxicants can be either hydrophilic (water-soluble) or lipophilic (fat-soluble). Sauna can help excrete both, since sweating triggers release from both sweat and sebaceous glands.
Though sweat is an important excretory pathway, it is likely that mechanisms for detoxification go far beyond sweating. These may include the entire array of beneficial adaptations to heat stress, including the repair or removal of damaged cells via HSPs and activation of FOXO3.infus
Sweating has also been demonstrated to increase excretion of toxicants such as organochlorinated pesticides (OCPs),[27] which have been shown to cause mitochondrial damage, oxidative stress, cell death, endocrine disruption, and epigenetic modification.s
Sauna-based treatment of individuals exposed to hexachlorobenzene (HCB) and polybrominated biphenyls (PBBs) led to a remission of symptoms and an average reduction of HCB body burden of 30% at post-treatment and 28% 3 months post-treatment. Mean reduction of polychlorinated biphenyl was 16% at post-treatment and 14% 3 months post-treatment.
Sauna use may very well be the single most powerful tool for detoxification available.

4. Reduces Rates of Heart and Cardiovascular Disease
Sauna bathing is inversely associated with the risk of sudden cardiac death, coronary heart disease (CHD), and cardiovascular disease (CVD) independent of conventional risk factors. A Finnish study (mentioned above) following 2,315 men for 20 years found that the risk of fatal CHD events was 23% lower for 2-3 sauna sessions per week and 48% lower for 4-7 times per week. Risk of dying from cardiovascular disease was 27% in the group using the sauna 2-3 times per week, and a whopping 50% lower for those using the sauna 4-7 times per week.[33]
Another study following 2,227 men for 26 years found that sauna use was associated with lower risk of cardiovascular mortality independent of cardiorespiratory fitness. That means the sauna was conferring benefits above and beyond exercise alone. The authors concluded that the combination of the two may confer additional survival benefits since those who had high cardiorespiratory fitness and high sauna use (3-7 times per week) had the lowest CVD and all-cause mortality. After adjusting for age, BMI, smoking status, Type II diabetes, cholesterol, current CHD, alcohol consumption, socioeconomic status, and C-reactive protein levels, those with high cardiorespiratory fitness and high sauna use had a 58% lower risk of CVD mortality and a 40% lower risk of all-cause mortality. Adjusted for age alone, the reduction in risk was 73% and 55%, respectively.
Sauna use improves vascular flow and endothelial function by increasing the expression of endothelial nitric oxide synthase (eNOS). This is important for other lifestyle diseases, too, since people with Type 2 diabetes and obesity also show impaired endothelial function.
Again, the biggest study on the subject ever done showed a 50% decreased risk of dying from cardiovascular vascular disease in those who use a sauna 4-7 times a week. There are few other therapies in existence that show this kind of effect.

5. Lowers Blood Pressure
Research has shown that sauna use in combination with exercise is more effective at lowering blood pressure than exercise alone.

6. Increases Weight Loss
Adding to this, we also have other lines of evidence suggesting a link between HSPs and fat loss. Mice with high expression of HSPs have lower body fat mass, better insulin tolerance and glucose clearance, less intramuscular lipid accumulation, more oxidative enzymes and higher number of mitochondria.[45]
How Saunas Help With Weight Loss
Sauna use can also modulate appetite. In one study, normal-weight patients with appetite loss increased ghrelin (a hormone associated with hunger ) concentrations, leading to normal daily caloric intake and feeding behavior. Obese patients, on the other hand, did not have an increase in ghrelin and instead, using the sauna reduced “abnormal feeding behavior” such as overeating and snacking between meals. Their body weight and body fat significantly decreased after two weeks of sauna therapy.[46]
Sauna uses increases metabolic rate and oxygen consumption similar to moderate exercise. This may help with weight maintenance for those unable to exercise due to illness or injury.

7. Increases Physical Performance, Endurance, and Energy
Cardiovascular improvements gained via hyperthermic conditioning – like increased plasma volume, increased red blood cells and blood flow to the heart – improve athletic endurance and performance. These benefits apply to athletes at all levels: highly trained, moderately trained, and untrained.
Hyperthermic conditioning improves thermoregulatory mechanisms, which means your body stays cooler and performs better at higher temperatures, like those induced during exercise.
Increased blood flow to skeletal muscles improves nutrient delivery, reducing reliance on glycogen stores during exercise. One study noted that heat acclimation reduced glycogen depletion during exercise by 40-50%.  In other words, sauna use seems to help the body perform exercise more efficiently and with greater ease.
The effects on performance have led some to call sauna use a “performance enhancing drug.”

8. Increases Muscle Growth
Sauna use increases muscle growth (hypertrophy) and reduces muscle breakdown.
HSPs repair damaged cells and help prevent future damage by reducing oxidative stress, which is a major cause of muscle degradation. This results in reduced muscle breakdown.
Sauna use causes a major increase in growth hormone levels. Depending on the temperature, duration, and frequency of sauna exposure, these increases are generally between 2- and 5-fold but one study showed that after two one-hour sessions per day at 80°C (176°F) for seven days, growth hormone levels increased 16-fold on the third day!
Growth hormone increases levels of insulin-like growth factor I (IGF-1), which increases protein synthesis and decreases protein breakdown, resulting in muscle hypertrophy. (Note: If you’re a longevity science geek like myself, and you are concerned about a link between GH or IGF-1 and longevity, remember that sauna use profoundly decreases all-cause mortality. So these spikes in these hormones appear to be only beneficial to health and longevity.)
Sauna use also increases insulin sensitivity. This results in improved uptake of amino acids into skeletal muscle, enhancing muscle growth. (And results in fewer nutrients ending up in fat cells.)
 
9. Faster Post-Workout Recovery
Lactic acid build-up in the muscles after exercise is reduced as the result of hyperthermic conditioning.
Sauna use reduces exercise-induced muscle damage and delayed-onset muscle soreness.
Researchers have found that infrared heat improves recovery of the neuromuscular system after maximal endurance performance.  
As mentioned above, sauna use enhances muscle regrowth and reduces oxidative stress after a period of immobilization. So don’t forget to make the sauna part of any injury recovery!
HSPs may protect against rhabdomyolysis, a serious condition caused by excessive muscle breakdown due to overuse which can cause kidney failure. Hyperthermic conditioning leads to higher expression of HSPs under both normal conditions and subsequent exposure to heat, so pre-conditioning is key here.
Sauna use is a potent tool for accelerates recovery in between exercise sessions.

10. Promotes Brain Performance, Neuron Repair, and Growth of New Brain Cells
Sauna use also increases brain-derived neurotrophic factor (BDNF), since heat stress in conjunction with exercise has been shown to increase expression more than exercise alone. BDNF increases the growth of new brain cells and improves the survival of existing ones. It increases neuroplasticity, which is important for learning and long-term memory.
Importantly, low BDNF has been linked with both depression and chronic fatigue syndrome (CFS).
BDNF increases from exercise, and this is thought to be a major reason why exercise is linked to improved brain health and protection from neurodegenerative disease. Everyone knows that exercise helps prevent muscle atrophy with aging, but few realize that it also prevents brain degeneration as much as it helps prevent muscle atrophy. Sauna also increases BDNF and sauna use has also been linked with hugely decreased rates of certain neurodegenerative diseases.
Other research has shown that sauna use has a huge impact on other hormones like norepinephrine and prolactin, which play roles in focus and attention, as well as promotes nerve myelin growth and nerve repair.
Sauna use significantly increases norepinephrine and prolactin levels, which has benefits for mental performance. During sauna, norepinephrine increases 2- to 4-fold, while prolactin increases from 2- to 10-fold.
Norepinephrine improves focus and attention. Heat stress also increases the capacity of norepinephrine to be stored for later use.
Prolactin promotes myelin growth. Myelin insulates nerve fibers and increases the speed at which nerve impulses are conducted, which makes your brain work faster. It is also important for repairing nerve cell damage.
In addition, “runner’s high” – the sense of euphoria that accompanies prolonged exercise – is thought to be related to heat stress, and research has shown that sauna use affects these same endorphin pathways.

11. Improves Skin Health
Passive heat therapy improves skin microvascular function, which means better nutrient delivery to skin cells.
Mild heat stress has anti-aging hormetic effects on the growth of human skin fibroblasts (cells in connective tissue that produce collagen and other fibers). In other words, it temporarily stresses your skin cells and induces them to build up their anti-oxidant defense systems and stimulating cell repair processes, which protect them from future stresses (like sun exposure or toxins).
Regular sauna use has a beneficial effect on skin health, improving hydration, maintaining surface pH, and resulting in less oil on the forehead of participants measured.
In short, sauna use is a powerful tool for improving your skin health.  
(Thank you Ari Whiten for providing the content of this article.)

Potential Hazards of Infrared Sauna Use
Although most of the people using saunas do not experience any troubles, there may be an odd case, where you may experience some adverse effects due to the high temperatures of the sauna, especially in the following situations:
Overheating causing heat stroke or heat exhaustion.
Dehydration that may be caused due to insufficient fluid intake.
Consuming alcohol during the sauna therapy session.
Toxins that are mobilized in the bloodstream because of detoxification.
Interference with certain medications.
Medical conditions that have been triggered.
Adverse effects on implants.
If you are healthy and are not taking any medications, the symptoms caused due to an overdose of sauna are usually heating effects such as overheating, dehydration, depletion of electrolytes, etc. And, if you suffer from any medical conditions or you are taking any prescribed medications, it is a good idea to check with your medical practitioner before undergoing sauna therapy.