Sauna for multiple sclerosis (heat sensitivity, Uhthoff phenomenon)
Evidence review
Overview
Heat is a recognized trigger of temporary neurological worsening in multiple sclerosis (Uhthoff phenomenon), and the hot bath test was once used diagnostically because it provokes signs in a substantial share of patients. In heat-sensitive patients, a single moderate Finnish sauna session raised core temperature more than in healthy controls and acutely worsened walking, chair rise, functional reach and a processing-speed test, with recovery within an hour. Persistent deficits after a hot bath test and a fatal hyperthermia in a hot bath have been reported. Sauna is not a studied or supported treatment for MS; heat exposure is a caution or contraindication.
Key findings
- Single Finnish sauna, 23 heat-sensitive MS vs 19 controls: larger core temperature rise (P=0.002) and worse walking (P<0.001), chair rise (P=0.005) and functional reach (P=0.04) immediately after; no effect at 1 day (Romberg 2012)
- Same sauna exposure worsened PASAT 3 s cognitive performance in MS (p=0.025), reversing within about 1 h (Hämäläinen 2012)
- Hot bath test provoked new signs in 38% of 13 patients (Tan 1994) and was abnormal in 35% of 23 with definite MS (Rolak 1985)
- Questionnaire, 125 patients: 90% reported worsening in a hot bath (Brenneis 1979)
- Four patients had prolonged neurological deficits after a hot bath test (Berger 1983, PMID 6600798); a man with MS died of hyperthermia, body temperature 105.7 F, after becoming trapped in a hot bath (Kohlmeier 2000, PMID 10990274)
Every study we reviewed
7 found harm
Each study was checked on PubMed. The colored edge shows the direction of the result. The research library lists 37 studies on multiple sclerosis, across all heat and cold therapies, including case reports and older work not graded here.
The effects of heat stress on physical functioning in persons with multiple sclerosis.
Romberg A et al. J Neurol Sci. 2012. PubMed 22647586 · DOI
- Who
- 23 heat-sensitive people with MS and 19 healthy controls
- What
- single moderate heat exposure in a dry Finnish sauna
- Protocol
- single session/wk
- Measured
- physical function (walking, chair rise, functional reach, balance) before, immediately, 1 h and 1 day after heat
- Result
- Core temperature rose more in MS than controls (P=0.002). Immediately after the sauna, MS participants performed worse than controls in walking (P<0.001), chair rise (P=0.005) and functional reach (P=0.04). No prolonged effects at 1 h or 1 day.
- Limitations
- single exposure; heat-sensitive volunteers only; small; healthy rather than MS controls
The effects of heat stress on cognition in persons with multiple sclerosis.
Hämäläinen P et al. Mult Scler. 2012. PubMed 21914688 · DOI
- Who
- 23 heat-sensitive people with MS and 19 healthy controls (same participants as Romberg 2012)
- What
- single moderate heat exposure in a Finnish sauna
- Protocol
- single session/wk
- Measured
- cognition (PASAT 3 s and 2 s, visual vigilance) before, during and after heat
- Result
- Core temperature rose more in MS than controls (p=0.002). Heat worsened PASAT 3 s performance in MS (p=0.025) but not other cognitive measures; performance returned almost to baseline 1 h after exposure.
- Limitations
- same cohort as Romberg 2012; single exposure; effect mild and reversible
Toward isolating perceptual and physiological contributors to heat sensitivity in multiple sclerosis: insights from a new experimental model.
English T et al. Eur J Appl Physiol. 2025. PubMed 40500533 · DOI · Free full text
- Who
- 7 people with relapsing-remitting MS, optic neuritis and heat-sensitive visual symptoms; 6 controls
- What
- passive heating with a hot water-perfused suit to raise gastrointestinal temperature by about 1.1 F (0.6 C), with cold vs hot packs on the lower back
- Protocol
- two sessions (crossover)/wk
- Measured
- visual symptoms, multifocal visual evoked potentials, contrast sensitivity
- Result
- Passive heating worsened visual symptoms in the affected eye (p=0.027) and reduced mf-VEP amplitude in the affected eye (p=0.007), similarly with cold or hot packs; reductions in the unaffected eye were greater in MS than controls (p=0.031). Local skin cooling did not prevent the heat-induced decrements.
- Limitations
- very small; experimental heating model; visual outcomes only
The hot bath test among Malaysian multiple sclerosis patients.
Tan CT et al. Med J Malaysia. 1994. PubMed 8057994
- Who
- Malaysian patients with clinically definite MS
- What
- hot bath test with evoked potentials before and after heating
- Protocol
- single test/wk
- Measured
- new neurological signs; evoked potentials
- Result
- 5 of 13 (38%) developed neurological changes with rising body temperature (average 0.46 new signs per patient); 4 had motor disturbances, 2 visual deterioration.
- Limitations
- diagnostic test, not therapy; small; positivity lower than reported in other populations
The hot bath test in multiple sclerosis: comparison with visual evoked responses and oligoclonal bands.
Rolak LA et al. Acta Neurol Scand. 1985. PubMed 4050319 · DOI
- Who
- patients with definite, probable or possible MS (20 prospective, 30 retrospective)
- What
- hot bath test
- Protocol
- single test/wk
- Measured
- abnormal (symptom-provoking) hot bath test
- Result
- Hot bath test abnormal in 8 of 23 with definite MS (35%) and 4 of 27 with probable or possible MS (15%).
- Limitations
- diagnostic study; partly retrospective; does not describe severity or duration of provoked signs
[Effect of exposure to different temperatures on the clinical manifestations of multiple sclerosis].
Zavalishin IA et al. Zh Nevropatol Psikhiatr Im S S Korsakova. 1983. PubMed 6858475
- Who
- patients with multiple sclerosis (Russian report)
- What
- thermal procedures: hot bath or drinking 1-2 glasses of hot water; also cooling
- Measured
- clinical manifestations of MS
- Result
- Hot baths and hot drinks worsened the clinical status; sharp cooling also worsened status, while moderate cooling without shivering improved it.
- Limitations
- abstract only, in Russian; no quantitative results reported
[On the temperature sensitivity of multiple sclerosis patients (author's transl)].
Brenneis M et al. Fortschr Neurol Psychiatr Grenzgeb. 1979. PubMed 256872
- Who
- people with MS answering a questionnaire (German report)
- What
- self-reported response to heating and cooling, including hot and cold baths
- Measured
- self-reported symptom change with heat or cold
- Result
- 93% reported marked sensitivity to heating; 90% reported worsening of neurological symptoms or general feeling in a hot bath; about half reported improvement in a cold bath.
- Limitations
- self-report; recall bias; no objective measures
Protocols used in the studies
Heat was applied to provoke or measure symptoms, not to treat: one moderate dry Finnish sauna session (temperature and duration not given in the abstracts), hot-bath tests (water temperature not given), and a hot water-perfused suit raising core temperature by about 1.1 F (0.6 C). No therapeutic sauna or heat protocol has been studied in MS.
What is still unknown
Whether brief, low-temperature heat exposure is safe for people with MS who are not heat-sensitive; whether pre-cooling or cooling garments make sauna use safe; no study has examined repeated sauna use in MS.
Safety
Cautions for sauna in this condition
- Heat raises core temperature more in people with MS than in controls and acutely worsens walking, balance-related tasks, cognition and vision (PMIDs 22647586, 21914688, 40500533).
- Neurological signs provoked by heat are usually transient, but prolonged deficits after a hot bath test have been reported in four patients (Berger 1983, PMID 6600798), and a review notes persistent deficits in some patients after induced hyperthermia (Guthrie 1995, PMID 7751837).
- Heat-induced weakness can prevent a person with MS from leaving hot water; fatal hyperthermia in a hot bath has been reported (Kohlmeier 2000, PMID 10990274). Sauna, hot tub and hot-bath use should be treated as a caution or contraindication, and never unsupervised.
- Cooling, not heating, is the studied symptomatic strategy for heat-sensitive MS; see the cold-modality entry for multiple sclerosis.
- See general-safety.
For clinicians
Suggested rationale
No published evidence supports sauna or whole-body heat as a treatment for multiple sclerosis. In heat-sensitive patients a single moderate Finnish sauna session acutely worsened walking, chair rise and functional reach compared with controls (Romberg 2012), and persistent deficits and a fatal hot-bath hyperthermia have been reported; heat exposure is a caution or contraindication, and this evidence does not support a letter of medical necessity for sauna.
Suggested wording only. The treating clinician decides whether it reflects their clinical judgment for this patient.
Typical ICD-10 codes: G35. Examples only; the clinician assigns the code.
What a letter of medical necessity should containWho can write it: physicians, NPs, PAs and others