Whole-body hyperthermia

What it is

Heat applications can be arranged as a ladder from mild to intense. The classic sauna heats the air to 80 to 90 degrees; these are short, intense stimuli on the skin, and the body core stays almost normal. The infrared cabin works at an air temperature of 40 to 60 degrees and warms the tissue directly via radiation, more gently and easier on the circulation.

Whole-body hyperthermia is the medical step above that. Under supervision, the core temperature is deliberately raised and held in the fever range for 1 to 2 hours. This is usually done with water-filtered infrared A, wIRA for short. The radiation passes through a layer of water that filters out exactly those components that stress the skin surface, similar to the way water vapor in the atmosphere filters sunlight. What remains is heat that penetrates deep into the tissue without overheating the skin.

How it is supposed to work

When the body core rises into the fever range, a whole orchestra responds. The blood vessels dilate, pulse and cardiac output rise, almost as with brisk walking, which is why heat is also regarded as passive cardiovascular training. The cells produce more heat shock proteins, molecular repair helpers that bring misfolded proteins back into shape. The immune system experiences a kind of practice alarm, as with real fever.

For mood there is a separate hypothesis: heat on the skin is said to reset the mood system via temperature-sensitive networks in the brainstem that are linked to serotonin. After the session a counter-regulation follows, the core temperature falls, and many people then sleep remarkably deeply. The principle of fever against melancholy is old, from Hippocrates to the fever therapy of the early twentieth century, only the dosing back then was brutal. Mild hyperthermia is the civilized granddaughter of this idea.

Heat as a lifestyle

The epidemiological foundation comes from Finnish sauna research. In the KIHD cohort, 2,315 men aged 42 to 60 were followed for a median of 20.7 years. Those who used the sauna 4 to 7 times a week had a markedly lower risk of sudden cardiac death than those who went once a week; the hazard ratio was 0.37. Similar associations were seen for cardiovascular and all-cause mortality. These are observational data, Finns do not use the sauna at random, but the dose-response relationship is remarkable.

Applied locally, wIRA also has an established place, for example in wound healing. A review found 7 prospective studies, 6 of them randomized, with more blood flow and oxygen in the tissue and fewer wound infections after surgery, 5.1 versus 12.1 percent. The review, however, comes from proponents of the method.

What patients report

From fibromyalgia research there is also the inside view. In interviews 12 weeks after treatment, all patients interviewed reported less perceived pain and more well-being. When the relief set in and how long it lasted, however, varied greatly. The longer the plateau phase at elevated core temperature lasted, the lower the pain in week 12. These are patient reports and a correlation analysis, not additional proof of efficacy.

Practitioners recommend heat regularly rather than heroically: drink enough, end the session before it becomes unpleasant, and observe the effect on your own sleep. The application is usually given as a course with several sessions.

What the studies show

Fibromyalgia (Langhorst, 2023)

41 patients were randomized to receive either 6 treatments with mild wIRA whole-body hyperthermia over 3 weeks or a sham treatment in which an insulating foil kept out most of the radiation. The maximum temperature averaged 38.7 degrees for about 15 minutes. Pain was significantly lower than in the sham group in week 4 and still in week 30.

Depression (Janssen, 2016)

In this double-blind study in JAMA Psychiatry, 34 adults with major depression not taking psychotropic drugs were randomized, and 29 were analyzed. A single session of active hyperthermia lowered scores on the Hamilton Depression Rating Scale compared with a sham treatment of equal length by 6.53 points in week 1 and still by 4.27 points in week 6. Side effects were mild.

Depression with psychotherapy (Mason, 2025)

30 people with depression all received cognitive behavioral therapy plus either hyperthermia with an infrared sauna device or a sham treatment. Both groups improved markedly; no advantage of the heat was discernible. The authors suspect that the sham treatment itself had an effect and consider further studies necessary.

Where the data stop

The good studies are small, 34 and 41 participants, and the depression findings have not been consistently replicated. Heat is hard to blind, even though in the depression study 71.4 percent of the sham group believed they had received the real treatment. Larger, independent studies are still pending.

The strong survival finding in oncology concerns regional hyperthermia of a tumor area, not the mild whole-body hyperthermia offered by private practices, and it applies only together with chemotherapy. For the frequently advertised applications of detoxification, chronic infections and general immune strengthening there are no controlled studies. Anyone who hears promises against cancer in a wellness context should become skeptical.

Status, approval and legal

Whole-body hyperthermia is a medical or physical-therapy procedure and is offered in Germany by clinics, rehabilitation facilities and private practices. Oncological hyperthermia, as an add-on to chemotherapy and radiotherapy, belongs exclusively in specialized clinics. According to reports, German rehabilitation clinics also routinely use the mild variant for pain, mood and recovery. Because the core temperature must be monitored, it belongs in experienced hands and not in self-directed use.

Safety

For people in good basic health the mild variant is well tolerated; the main strain is on the circulation. In an analysis of 855 sessions in 397 cancer patients, headache occurred in 54.9 percent, skin reactions in 11.7 percent and cardiovascular effects in 9.4 percent; there were no serious incidents. People with unstable heart disease, very low blood pressure or recent thromboses, as well as pregnant women, should not go into the heat without a check. The most common mistake is too little fluid, and medications that affect temperature regulation should be discussed with a physician beforehand.

Sources

• Langhorst J et al., J Clin Med 2023
• Janssen CW et al., JAMA Psychiatry 2016
• Mason AE et al., Glob Adv Integr Med Health 2025
• Issels RD et al., JAMA Oncol 2018
• Hohneck AL et al., Cancers 2025
• Laukkanen T et al., JAMA Intern Med 2015
• Hoffmann G et al., Ger Med Sci 2016
• Langhorst A, Langhorst J, Schmerz 2023
• Öznur Ö et al., Biomedicines 2023