For doctors, nurse practitioners and physician assistants
The evidence, short and honest, so you can decide.
You do not have to be a physician to write the letter.
What you are attesting to
That, in your clinical judgment, the treatment is recommended primarily to treat a diagnosed condition. You are not certifying tax eligibility; the plan administrator and the patient carry that.
What you are not attesting to
That the purchase qualifies under the tax code, that a specific product is required, or that the patient would not have bought it otherwise. Only the patient can answer that last one.
How strong the evidence is
Grades describe the research, not the therapy. A and B need randomized or controlled trials in patients showing benefit; C means early studies, cohort associations or mixed results; D means not yet studied in patients, or no benefit found. The grade and the studies behind it are on every page.
Entries with grade A or B evidence
These have randomized or controlled trials in patients showing benefit. The full library, including emerging evidence, is on the evidence page.
Fibromyalgia
Randomized trials of mild water-filtered infrared whole-body hyperthermia, a clinic-delivered form of systemic heat, reduced fibromyalgia pain versus multimodal rehabilitation alone and versus sham hyperthermia; in the sham-controlled trial the difference was significant at weeks 4 and 30 but not at week 12, and responder rates did not differ. The only controlled sauna study is small and non-randomized: 12 mild sauna baths raised pressure pain thresholds by 22% versus 8% with exercise-pool sessions. Waon (140 F far-infrared sauna), sauna-plus-aquatic-exercise and hot-water immersion studies also report pain and FIQ improvements, but these were uncontrolled and small (8-44 patients). Sauna-specific randomized data are lacking.
8 studies · reviewed November 8, 2026
Allergic rhinitis
In a small randomized trial of Thai adults with skin-test-confirmed allergic rhinitis, 6 weeks of sauna sessions 3 days per week increased peak nasal inspiratory flow and FEV1 compared with education alone; symptom scores were not reported in the abstract. A second Thai trial randomized 64 patients to steam baths with or without herbs, 30 minutes 3 times a week for 4 weeks; nasal symptoms fell in both groups with no difference between them, but without a no-steam control the trial cannot separate a heat effect from time or expectation. A small Japanese crossover study found that one 10-minute warm mist sauna relieved nasal congestion and increased nasal volume for 30-90 minutes, longer than an ordinary 104 F tub bath; it measured acute effects only.
3 studies · reviewed November 8, 2026
Ankylosing spondylitis / axial spondyloarthritis
In a German randomized trial of 35 inpatients with ankylosing spondylitis, adding six sessions of water-filtered infrared-A whole-body hyperthermia (a clinic radiant-heat device) to physical therapy gave greater pain relief, less analgesic use and improvements in BASDAI and BASFI lasting up to 3-6 months, while HAQ did not change. In a small infrared-sauna pilot, pain and stiffness fell during sessions without increased disease activity. A randomized spa-exercise program that included sauna at one site improved a pooled symptom index at 4 weeks, but sauna's own contribution is unknown. Mechanistic studies report lower pro-inflammatory cytokines after whole-body hyperthermia and no cortisol or lymphocyte change after a single hot bath.
7 studies · reviewed November 8, 2026
Chronic heart failure
Most trials in chronic heart failure tested Waon therapy, a hospital-based protocol developed in Japan: a far-infrared dry sauna at 140 F (60 C) for 15 minutes followed by 30 minutes of blanket rest, given once daily, usually 5 days a week, for 2 to 4 weeks alongside guideline medical therapy. Small randomized and controlled trials (n=30-188), mostly from one Japanese research network, report improvements in NYHA class, BNP, endothelial function, heart rate variability, ventricular ectopy and exercise capacity; a meta-analysis found lower BNP and a small LVEF gain (about 1.5 points). The largest multicenter RCT (WAON-CHF, n=149) did not meet its primary BNP endpoint, though walk distance, cardiothoracic ratio and NYHA class improved more than with medical therapy alone, and its neurohumoral subanalysis found no between-group differences. Outside this setting the evidence is limited to small studies: 140 F sauna in US and HFpEF pilots, single exposures to 176 F Finnish sauna and to warm-water immersion, leg-only heating added to cardiac rehabilitation, a German home hydrotherapy crossover trial, and a small Japanese controlled study in which 2 weeks of half-body hot-spring immersion at 104 F was followed by lower BNP and pulse wave velocity than daily showering.
27 studies · reviewed November 8, 2026
Chronic tension-type headache
In a New Zealand randomized trial, adults with chronic tension-type headache who used a sauna regularly for 8 weeks in addition to advice and education had a greater reduction in headache intensity than those receiving advice alone. Headache duration, sleep, depression and headache disability did not differ between groups. The trial has not been replicated.
1 study · reviewed November 8, 2026
Coronary artery disease (chronic ischemic heart disease)
In the KIHD cohort, more frequent Finnish sauna use was associated with lower risk of sudden cardiac death, fatal coronary heart disease and cardiovascular mortality in a dose-dependent way, and in a Japanese cohort of 30,076 adults almost daily hot-tub bathing was associated with lower incident coronary heart disease; these are associations in general populations, not trials in patients with CAD, and in the KIHD analysis that included women the association was not significant in women alone. In adults with stable CAD, single sauna and warm-footbath sessions acutely improved brachial flow-mediated dilation and coronary flow reserve, but an 8-week randomized trial (4 sessions/week) found no improvement in endothelial function, arterial stiffness or blood pressure. A small non-randomized Japanese study reported improved myocardial perfusion with Waon therapy in chronic total coronary occlusion, and an older German randomized rehabilitation study after bypass surgery found similar LVEF gains with sauna or walking. Older Japanese studies from one group measured invasive hemodynamics during a single 5-minute 107.6 F (42 C) hot-water bath after myocardial infarction: pulmonary arterial and wedge pressures rose during the bath, most in patients with extensive anterior infarction and lower ejection fraction, and both cardiac events that occurred during bathing in a 70-patient series were in patients with lower cardiac function.
14 studies · reviewed November 8, 2026
Essential (primary) hypertension
In the Kuopio Ischaemic Heart Disease (KIHD) cohort, men who used a sauna 4-7 times per week had a lower risk of developing hypertension than men who used it once weekly; this is an association in initially normotensive men. Single sauna or hot-water immersion sessions acutely lower blood pressure in hypertensive patients (including central pressure after an ordinary home bath, without a difference in night-time pressure), but in a randomized crossover trial a single 185-194 F sauna session alone did not lower 24-hour ambulatory pressure; only exercise followed by sauna did. Older uncontrolled and non-randomized German studies reported lower resting pressure after months of regular sauna. Controlled evidence for a sustained effect is limited: an 8-week RCT found lower systolic pressure when sauna was added to exercise in adults with cardiovascular risk factors, while an 8-week sham-controlled RCT of home lower-leg hot-water immersion in hypertensive women found no change in ambulatory pressure. Meta-analyses of heat-therapy trials report modest systolic reductions (about 2-4 mmHg), but the most recent RCT-only meta-analysis found no significant overall effect on systolic or diastolic pressure.
17 studies · reviewed November 8, 2026
Major depressive disorder
Whole-body hyperthermia (raising core temperature to about 101.3 F) and hyperthermic baths have produced rapid reductions in depressive symptoms in some small randomized trials of adults with major depressive disorder. The best-controlled trial used a single session against a credible sham and found a HAM-D advantage that persisted for 6 weeks; secondary analyses of that trial linked response to an acute rise in interleukin-6 (Flux 2023, PMID 37085494; Mac Giollabhui 2024, PMID 38677624). The hot-water bath trials are weaker than they first appear: the sham-controlled trial was significant only with one-sided testing, and the trial against exercise was open label, with its 2-week benefit not significant per protocol or at 8 weeks. A 2025 randomized trial in which both arms also received CBT found large improvements in both the active and sham arms with no added benefit detectable, and a 2019 systematic review of 7 small studies judged the evidence insufficient for general recommendations. Evidence is limited to short follow-up, small samples and mostly medication-free or adjunctive settings. In two analyses of the Japanese JAGES cohort of older adults, daily home tub bathing was associated with fewer new cases of depressive symptoms over 3 and 6 years, significantly in winter; these are associations with screening-scale scores, not trials in diagnosed depression.
9 studies · reviewed November 8, 2026
Peripheral arterial disease of the lower extremities
Waon therapy (140 F far-infrared sauna) was tested in a small randomized trial of patients with peripheral arterial disease, in which leg pain, ankle-brachial index and 6-minute walk distance improved within the Waon group but not in controls after 6 weeks; the groups were not compared directly, and a review found the between-group differences not significant. In a 12-week RCT, hot-water spa bathing at about 102 F and supervised exercise produced similar gains in walking distance and resting blood pressure, without change in ankle-brachial index; the trial was small and had no untreated control. A single 30-minute waist-level hot-water immersion markedly increased leg blood flow and lowered blood pressure in PAD patients. A 2021 systematic review found that walking distance and ABI improved with whole-body hot-water immersion but not significantly with Waon therapy.
5 studies · reviewed November 8, 2026
Psoriatic arthritis
In a German randomized trial of 35 inpatients with psoriatic arthritis, adding six sessions of water-filtered infrared-A whole-body hyperthermia (a clinic radiant-heat device) to standardized physical therapy gave greater pain relief and less analgesic use than physical therapy alone, and DAS28 fell only in the hyperthermia group, with effects reported up to 6 months. Skin involvement (PASI) and ESR/CRP did not change in either group. The trial was small and unblinded, and no study has tested a conventional or infrared sauna in psoriatic arthritis.
1 study · reviewed November 8, 2026
What a letter should contain
- The diagnosis and an ICD-10 code.
- The specific treatment (sauna, infrared heat, or cold-water immersion) and how it addresses the condition.
- The protocol: temperature, minutes per session, sessions per week.
- A statement that it is recommended primarily to treat the condition, not for general health.
- Duration of need and a reassessment date. Many plans want a new letter every 12 months.
- Your name, credential (MD, DO, NP, PA or other), license or NPI number, signature and date.
The IRS has said a note based on self-reported information does not make a general-health expense medical. A letter from the clinician who actually manages the condition is the strongest documentation a patient can have. See the rules.
Safety first
Template you may adapt
LETTER OF MEDICAL NECESSITY Date: [date] Patient: [full name] Date of birth: [DOB] Diagnosis: [condition] (ICD-10 [code]), diagnosed [date / ongoing] Recommended treatment: [regular Finnish sauna / infrared (Waon-type) heat therapy / cold-water immersion] Protocol: [temperature] °F, [minutes] minutes per session, [sessions] sessions per week, for [months] months, then reassessment. Clinical rationale: In my clinical judgment, this treatment is recommended primarily to treat [condition] in this patient. [One or two sentences on the patient's current status, prior or ongoing treatment, and the expected benefit.] Published evidence considered: [first author, year, journal; e.g., from the SaunaLMN evidence page for this condition]. This recommendation is made for the treatment of the diagnosis above and not for general health or wellness. I have reviewed relevant contraindications with the patient: [notes]. Duration of need: [12 months], to be reassessed on [date]. [Clinician name, credentials (MD, DO, NP, PA)] [Practice, address, phone] NPI: [number] Signature: ______________________