Far infrared sauna health benefits include improvements to these illnesses: [1, 2]
- Removes obesogen toxins
- Cardiovascular diseases
- Rheumatoid arthritis
- Tension headaches
- Dementia and Alzheimer’s
- Chronic kidney disease
- Diabetes mellitus
- Chronic fatigue
- Ankylosing spondylitis: arthritis in the spine or large joints.
- Chronic pain
- Cholesterol levels: Reduce bad LDL and increased good HDL
- Vascular endothelial dysfunction: Damaged cells that line the blood vessels.
- Hay fever (allergic rhinitis)
- COPD (chronic obstructive pulmonary disease)
- Ischemia reperfusion injuries
- High blood pressure (hypertension)
- Heart failure
- Toxic poisoning from heavy metals: petrochemicals, lead, mercury, cadmium, arsenic
- Organochlorine pesticide poisoning
- Xenobiotics: flame retardants, bisphenol-A (BPA), and phthalates
- Psychological stress
- Poor sleep
- Poor neuromuscular performance after intensive athletic training 
- Peripheral artery disease (peripheral vascular disease) 
Far Infrared Saunas vs. Traditional Saunas
According to this study , traditional saunas are heated to 176 – 212°F which is simply too hot for many people to enjoy. Whereas, the infrared saunas are only heated to 113- 140°F which is much more comfortable. 
However, one Finnish sauna manufacturer said that average traditional saunas operate between 160-190°F, and that the permissible UL Testing limit is 194 °F. I have not verified this, but it seems reasonable to me.
Additionally, the 212°F mentioned in the study, probably refers to the steam that is created when water is thrown on the hot rocks. That is a localized heat that is dissipated throughout the sauna, and not the actual temperature of the sauna.
Also, keep in mind that heat rises, so the lower area of a sauna won’t be as hot as the upper areas.
How Do The Humidity Levels Compare?
The traditional sauna manufacturers say that the humidity is about 12% before steam is created on the hot rocks, which can raise the humidity to about 35%. They incorrectly claim that the humidity in the far infrared saunas is practically zero, because you don’t throw water on hot rocks.
Well, both types of saunas have vent holes to permit fresh air to enter. Which means that the infrared saunas are being humidified by the household air as it enters the sauna. That probably means that the actual humidity level is lower than the household humidity.
So, as a wild guess on my part. If household humidity is 40%, as the air is heated, the humidity would drop to maybe 20%? Whatever level it drops to, it should stay pretty consistent.
Since the infrared sauna temperature is lower than the traditional sauna, not as much humidity would be lost. Which means that the infrared sauna should stay above the 12% “dry” traditional sauna humidity level.
Far Infrared Saunas Produce More Sweat Than Traditional Saunas
Surprisingly, the low temperatures of the far infrared saunas also produce more sweat than the traditional saunas.
This is the result of the far infrared effects penetrating deeper into the skin. Far infrared can reach into the body 2–3 cm (0.79 – 1.18 inches).  Whereas the traditional sauna only provides heat to the skin surface.
In other words, the infrared heaters are heating a larger effective surface area, and therefore more sweat.
Far infra red saunas are more effective at evaporating sweat than traditional saunas. That’s because the higher humidity (when steam is created) in traditional saunas condenses on the skin. Which prevents the evaporation of the sweat. 
Approximately 30-50% of the water dripping off your body in a traditional sauna is not sweat, but condensed water from the steam. 
Sauna Use Provides The Benefits Of Moderate Walking
The cardiovascular effects provided by walking: increased heart rate and volume of blood pumped, sweating, and vasodilation are all obtained by sitting in a sauna. 
So, anyone with osteoarthritis or any respiratory problems (COPD), or cardiovascular health problems, should consider using the far-infrared sauna.
Weight Loss From Higher Metabolism
As your core body temperature rises your body naturally tries to cool off by sweating. Which requires the heart to pump more blood and burn more calories. Which leads to weight loss.
Sweating Removes Toxic Chemicals (Obesogens) That Prevent Fat Loss
Modern living brings us into contact with heavy metals and chemicals that interrupts the endocrine system and prevents fat from being removed from the body. The term for these chemicals is: obesogens. 
Basically the toxins make the fat cells toxic and they don’t function properly. By removing the toxins the fat cells can now be removed trough the body’s normal processes.
Obesogens include mercury, arsenic, cadmium, lead, BPA (bisphenol A), and probably cigarette smoke, flame retardants, some pesticides, air pollution, Polychlorinated biphenyls (PCBs), Tributyltin (used in PVC pipe) and many more common chemicals.
Fortunately, sweating can remove many obesogens. Such as mercury, lead, arsenic, and cadmium.  Sweating can even remove the chemicals used to make meth. 
If you have done everything to lose weight and and failed…get into a far infrared sauna today.
Got Fat? High Blood Pressure? Diabetes? Do This…
Anyone who is obese, diabetic, has high blood pressure (hypertension) or hyperlipidemia (high cholesterol and triglycerides) has endothelial dysfunction. 
Endothelial dysfunction means that the inner lining of the blood vessels are not able to expand and contract properly, or to perform their other functions.
It is the expansion and contraction of the little blood vessels (Arterioles) that provide just the right amount of blood to the body tissues.
Poor functioning of these blood vessels can result in high blood pressure, or a lack of blood flow to the body tissues. Which causes all kinds of problems. Like atherosclerosis, heart attacks, and diabetic amputations.
Get yourself into a far infra-red sauna for 15 minutes at least four times per week. Not only will your health improve, but you will enjoy the time relaxing and the reduced stress.
Diabetes Mellitus and Peripheral Artery Disease
Reduced blood supply to body tissues and body cells is called tissue ischemia. This results in a lack of oxygen to the cells, causing them to die. For diabetics this is the cause of gangrene, which results in amputations.
Far infrared therapy has been shown to increase micro blood circulation. Which can help prevent cell death, and gangrene. 
Peripheral artery disease is the result of partially blocked blood vessels which leads to less oxygen to the legs or arms. This causes pain, increases the chances of a stroke 3X, and can also lead to gangrene and amputations.
Can You Lose Weight Sitting in A Far Infrared Sauna?
In this study, obese patients lost a significant amount of fat and weight during two weeks of sauna use.  Better yet, they didn’t feel any hungrier, because the food craving ghrelin hormone level did not increase.
Chronic Pain Relief From Far Infra-Red Therapy
In this study the chronic pain patients reported less pain, depression and anger by using the sauna therapy. They were treated everyday for a month. At the 2 year check-up, 77% of the patients had returned to work. 
Fibromyalgia Pain Relief with Waon Therapy
Waon therapy is simply far infra-red sauna therapy where the person is kept warm with a blanket for 30 minutes after their sauna session.  This provides for a gradual decrease in body heat after the sauna therapy.
The patients were treated either 2 days per week or 5 days per week, for 15 minutes each session. 
All 13 women had approximately half as much pain after the first sauna session.
Chronic Heart Failure and Ventricular Arrhythmias
After two weeks of sauna use 17 out of 20 people with chronic heart failure had fewer heart disease symptoms. 
That was the result from better vascular endothelial function. Which means the endothelial cells that line the blood vessels inside the heart were functioning better.
Among other functions, the endothelial cells release substances which regulate the relaxation and contraction of the blood vessels. The end result was that the heart also functions better.
Another study found that sauna use reduced ventricular arrhythmias.  Which simply means that the heart is beating too fast, and that can lead to lower blood circulation in the brain and heart attacks.
In a third study, 13 of the 15 patients had chronic systolic heart failure. They had fewer symptoms after treatment. Including lower systolic blood pressure while maintaining their heart rate.  Those patients also performed better when tested on their ability to exercise.
A Far infrared Sauna Reduces Oxidative Stress and Prevents Atherosclerosis.
A study of 28 people with heart disease were treated for 15 minutes per day for two weeks with far infrared saunas.  Their systolic blood pressure was lowered and so was the amount of oxidative stress (fewer free radicals).
Atherosclerosis is where cholesterol plaque builds up on the walls of the blood vessels and causes blood clots.
Chronic Fatigue Syndrome
This study of two people with chronic fatigue syndrome were first treated with prednisolone, which was ineffective. 
They received 35 sessions of far infra-red sauna therapy, and then one or two sessions per week for a year.
These two patients suffered with pain, poor sleep, and fevers, in addition to fatigue. All of which was greatly improved after 15-25 sauna sessions.
They were back to normal living within six months.
In this study ceramic disks were used to treat the women with far-infrared light therapy. However, using a sauna would be more convenient and comfortable.
As expected, the therapy increased blood flow to the breasts. Which increased lactation for 75% of the women. 
Speedy Skin Wound Healing
In a study using rats, wound healing was much faster. This was due to an increase in fibroblasts producing the Transforming Growth Factor-Beta1 (TGF-β1). Which, in turn, chemically signals the cells to grow and multiply, among many other functions. 
Rheumatoid Arthritis and Ankylosing Spondylitis Arthritis Relief
For each type of arthritis, there were 17 patients. They had somewhat less fatigue, pain and stiffness during their two sauna sessions each week for four weeks. However, these were not major improvements. 
End-Stage Renal Disease (ESRD) and Hemodialysis Patients
These patients were treated with far infra-red therapy on the appropriate acupressure points.  In my personal non-doctor opinion, these patients would probably have had better results if they had been treated in a FIR sauna.
However, they did have less fatigue, stress and depression from their far infra-red therapy. Also, the study mentioned un-specified improved autonomic nervous system (ANS) functions.
Phantom Limb Pain Removed with Far Infra-red Light Therapy
After suffering for ten years after an amputation, a patient finally got nearly total pain relief within six months.  He received two 40 minute treatments per week.
After one month his pain score dropped from a 9 to a 4. The next month, his pain score had dropped to a 2 or 3.
Not only did the amount of pain decrease, but the duration of the pain also decreased.
After six months he seldom had any pain. When it did occur, his pain score was only a 1 or 2 and the pain only lasted for a few seconds.
Infrared Sauna Lyme Disease Hoax?
There is no direct medical evidence that Lyme disease can be treated by far infrared sauna use.  However, that same study says to treat yourself with the infrared sauna to remove the toxins that create the same symptoms as Lyme disease.
Essentially, they are saying that many people think they have Lyme disease, but that they may actually be suffering from chemical toxicity. That toxicity is the result of all the chemicals we come into contact with every day.
That same study quotes another study which says more than 100,000 new chemicals have been created in recent years. All those new chemicals are in products we use regularly.
So get in that far infrared sauna and sweat those chemicals out.
References and Source Material
 Infrared sauna in patients with rheumatoid arthritis and ankylosing spondylitis. A pilot study showing good tolerance, short-term improvement of pain and stiffness, and a trend towards long-term beneficial effects.