Far Infrared Therapy
in Osteoarthritis.
A mechanistic and clinical review, with explicit positioning on structural and cartilage claims.
A small knee-OA trial reported pain and effusion improvements. Replication is needed.
Local plaster outcomes should not be presented as whole-body sauna outcomes.
Structural findings remain preclinical. Exercise and established care stay central.
The evidence, in context.
Background. Osteoarthritis (OA) is a whole-joint disease involving cartilage loss, subchondral bone remodeling, synovial inflammation, and periarticular muscle and tendon changes. Management centers on exercise, weight management, and self-management, with thermal interventions conditionally recommended by the American College of Rheumatology for small improvements in pain and function (Kolasinski et al. 2020).
Evidence. The most direct human evidence for far infrared (FIR) in OA is a single-blind, placebo-controlled randomized trial of an FIR-emitting plaster in knee OA, which reported a reduction in pain and fewer ultrasound-detected effusions over four weeks (Bagnato et al. 2012). Trials of other infrared wavelengths in OA have been negative (Tsagkaris et al. 2022).
A 2026 rat study reported FIR-induced pain relief with preservation of cartilage and suppression of subchondral osteoclastogenesis (Qin et al. 2026), and FIR down-regulates inflammatory gene networks in experimental arthritis (Chen et al. 2022).
Positioning. FIR may be considered as a comfort adjunct within established care. Human evidence for structural modification of the OA joint does not exist, and FIR should not be represented as regenerating cartilage or delaying joint replacement.
More than cartilage.
Osteoarthritis is the most common joint disorder and a leading cause of disability in older adults. Once viewed as simple wear of articular cartilage, OA is now understood as a disease of the whole joint organ.
Cartilage degradation, subchondral bone sclerosis and marrow lesions, osteophyte formation, low-grade synovitis, and weakness of the surrounding musculature all contribute to pain and loss of function.
The 2019 ACR/Arthritis Foundation guideline strongly recommends exercise, weight loss in knee and hip OA, self-management programs, and tai chi. Thermal interventions, acupuncture, and cognitive behavioral therapy receive conditional recommendations (Kolasinski et al. 2020).
Because pain and morning stiffness can limit exercise adherence, making movement more comfortable has practical value even when direct pain relief is modest.
Why warmth is being studied.
Synovial inflammation
Synovitis is present in a majority of symptomatic OA knees and correlates with pain. NF-κB and MAPK signaling drive cytokine and protease production in synovium and cartilage.
Subchondral bone
Increased osteoclast activity and abnormal remodeling of bone beneath the cartilage contribute to pain and progression of cartilage damage.
Periarticular stiffness
Collagen-rich capsule, ligament, and tendon tissues stiffen with disuse. Therapeutic heating increases collagen extensibility, particularly when combined with stretch (Lehmann et al. 1970).
Perfusion and pain processing
Reduced microvascular function is a proposed contributor to OA. Central sensitization in some patients also helps explain why imaging severity and pain do not always match.
Delivery changes the question.
Far infrared radiation (approximately 4–14 µm) is absorbed predominantly by water in superficial tissues. Two delivery formats are relevant to OA.
FIR sauna
Whole-body FIR, such as the Relax Sauna, uses active emitters and a head-out design. The supplied product specifications describe PTC semiconductor emitters, 95–99% emissivity, and a 9.4 µm peak.
Whole-body heating engages systemic autonomic and vascular responses.
Mineral emitters
Mineral-based FIR plasters, wraps, and topicals provide prolonged low-intensity exposure at one joint by re-radiating body heat.
The positive OA-specific randomized trial used this local format.
Plaster findings are not sauna outcomes. Evidence should not be transferred between delivery formats without qualification (Bagnato et al. 2012).
A localized plaster.
A promising early result.
Bagnato et al. 2012 · Single-blind randomized trial · 64 enrolled · 60 completers · Four weeks
Patients with primary knee OA and persistent pain (VAS ≥40 mm) despite acetaminophen or NSAIDs were assigned to an FIR-emitting mineral plaster or an identical plaster without the active minerals.
The plaster was applied behind the knee for 12 hours daily, five days per week, for four weeks (Bagnato et al. 2012).
The reported effect size was −1.38 at one month. No adverse events occurred.
This was a small, single-center, four-week trial with no long-term follow-up. WOMAC and Lequesne outcomes were not reported. The published report contains internal numerical inconsistencies, and devices came from a commercial source.
The finding requires replication before it can be considered established.
Other infrared wavelengths
A systematic review identified three OA trials comprising 276 patients (Tsagkaris et al. 2022). The FIR plaster trial was positive; an 890 nm near-infrared source and a 10.6 µm infrared laser found no significant effect. Wavelength, intensity, and duration matter.
Conventional thermotherapy
A Cochrane review found three small, low-quality trials. Hot packs showed no benefit over placebo or cold for edema; ice massage improved quadriceps strength and range of motion (Brosseau et al. 2003).
Thermal interventions still receive a conditional ACR recommendation based on low risk, low cost, and patient preference (Kolasinski et al. 2020). Differences in heat transfer and duration limit direct comparisons with FIR.
Whole-body FIR in OA
No controlled trial has evaluated whole-body FIR sauna specifically in OA. In rheumatoid arthritis and ankylosing spondylitis, infrared sauna produced immediate pain and stiffness reductions after sessions, with good tolerance, although four-week changes were not significant (Oosterveld et al. 2009).
Traditional Finnish sauna cohort data are excluded here as a different modality.
The research, side by side.
| Study | Population / Model | Intervention | Key Finding | Evidence Tier |
|---|---|---|---|---|
| Bagnato 2012 | Knee OA; 60 completers | FIR plaster vs placebo; 4 weeks | VAS 80→60 vs 79→73 mm; effusion 80%→40% in FIR arm; no adverse events | Direct, single-blind RCT |
| Tsagkaris 2022 | Review; 3 OA trials, 276 patients | FIR plaster, 890 nm NIR, 10.6 µm laser | Plaster positive; NIR and laser found no significant effect | Systematic review; mixed |
| Kolasinski 2020 | Hand, hip, and knee OA | Heat or cold | Conditional recommendation for pain and function | Guideline |
| Brosseau 2003 | Review; 3 RCTs, 179 patients | Hot packs, cold packs, ice massage | Hot packs showed no edema benefit; limited evidence | Cochrane review |
| Qin 2026 | MIA-induced OA in rats | Daily FIR, 30–60 minutes | Pain relief; cartilage and bone findings; reduced osteoclastogenesis | Animal |
| Chen 2022 | Adjuvant-induced arthritis in rats | FIR, 30 minutes | 27/370 inflammatory genes down; NF-κB, MAPK, PI3K-Akt suppressed | Animal inflammatory model |
| Hojo 2003 | Chondrocyte cell line | Heat, 39–45°C for 15–30 minutes | Improved viability and metabolism at ≤41°C; harm at ≥43°C for 30 minutes | In vitro |
| Bagabir 2025 | Human, heat-controlled three-arm RCT | FIR vs heat vs control | Vascular-function findings linked to NRF2 pathways | Mechanistic; not OA-specific |
Mechanisms worth investigating.
Subchondral bone and cartilage
In a monosodium iodoacetate rat model, daily FIR produced progressive pain relief and improved bone mineral density and cartilage integrity, with suppression of subchondral osteoclastogenesis.
In vitro, FIR inhibited RANKL-driven osteoclast differentiation by disrupting F-actin ring formation and modulating MAPK/c-Fos/NFATc1 signaling (Qin et al. 2026). Effects were strongest at days 7 and 14 and attenuated by day 28. These structural findings have not been tested in humans.
Inflammatory signaling
In adjuvant-induced arthritis, FIR improved clinical scores and down-regulated 27 of 370 inflammation- and autoimmunity-related genes, with suppression of NF-κB, MAPK, and PI3K-Akt pathways (Chen et al. 2022).
This inflammatory model differs from lower-grade OA synovitis. It supports a mechanism, not OA efficacy. Reduced effusion in the Bagnato trial is consistent with an anti-inflammatory effect.
Thermal dose and cartilage cells
In cultured chondrocytes, heating to 41°C or below increased viability and proteoglycan metabolism; 43°C or above for 30 minutes was harmful (Hojo et al. 2003).
Cell-culture temperatures are not sauna instructions. These findings do not establish a safe sauna setting, target body temperature, or treatment dose.
Perfusion and vascular signaling
FIR increases endothelial nitric oxide production through CaMKII-mediated eNOS phosphorylation (Park et al. 2013). A heat-controlled randomized trial reported FIR-specific endothelial-function and arterial-stiffness improvements via NRF2 pathways (Bagabir et al. 2025).
Improved periarticular perfusion remains a plausible, unmeasured contributor to OA symptom relief.
Stiffness and exercise readiness
Heating increases collagenous-tissue extensibility (Lehmann et al. 1970). Used before exercise or stretching, FIR may make movement more comfortable—an indirect pathway aligned with first-line care.
Clear limits on what we claim.
- FIR does not regenerate cartilage, reverse joint-space narrowing, or modify human OA joint structure. Structural findings exist only in animal models.
- FIR does not replace exercise, weight management, physical therapy, prescribed care, or timely orthopedic evaluation.
- FIR has not been shown to delay or prevent joint replacement.
- Plaster findings are not sauna outcomes, and results from other infrared wavelengths are not automatically FIR outcomes.
- Animal and cell findings are mechanistic evidence, not proof of clinical benefit.
Designing a definitive trial.
Adults with symptomatic knee OA, Kellgren–Lawrence grade 2–3, stratified by synovitis on ultrasound or MRI.
Local and/or whole-body FIR versus sham emitter, both with a standardized exercise program.
WOMAC or KOOS pain and function at 12 weeks.
Chair-stand and walking tests, synovitis and effusion imaging, exercise adherence, and analgesic use, with 6- and 12-month follow-up.
Wavelength, irradiance, skin temperature, and daily exposure time for each delivery format.
Clinical guidance.
Claims and uses that exceed the evidence.
- Heat on a suddenly hot, red, or markedly swollen joint before medical assessment
- Cartilage-regeneration or joint-preservation claims
- Replacing exercise, weight management, or orthopedic referral when locking, giving way, or rapid progression occurs
- Local heat over reduced sensation, broken skin, or infection
- Unsupervised whole-body heating with unstable cardiovascular disease
Comfort within a broader care plan.
- A comfort adjunct when stiffness or pain limits exercise
- Individual clinician guidance on whether whole-body heating is appropriate
- Clear acknowledgment that local-emitter evidence is device- and protocol-specific
- Tracking pain, stiffness, walking tolerance, and analgesic use over four to six weeks for discussion with a clinician
No OA-specific whole-body FIR schedule has been validated. Session duration and frequency should not be presented as an evidence-based OA treatment protocol.
Promising research.
Established care comes first.
One small randomized trial supports local FIR for knee OA pain. Animal research identifies plausible structural and anti-inflammatory mechanisms, and thermal interventions carry a conditional guideline recommendation.
Other infrared trials have been negative, and no human study has demonstrated structural benefit.
FIR is best discussed as a possible patient-directed comfort adjunct alongside exercise and established care, while stronger trials with validated outcomes are undertaken.
References & further reading
- Bagabir H, Mohammad OA, Lang C, et al. Far infrared therapy improves vascular function by enhancing endothelial function and decreasing arterial stiffness via cytoprotective pathways. Free Radic Biol Med. 2025;241:438-446. View reference.
- Bagnato GL, Miceli G, Atteritano M, Marino N, Bagnato GF. Far infrared emitting plaster in knee osteoarthritis: a single blinded, randomised clinical trial. Reumatismo. 2012;64(6):388-394. View reference.
- Brosseau L, Yonge KA, Robinson V, et al. Thermotherapy for treatment of osteoarthritis. Cochrane Database Syst Rev. 2003;(4):CD004522. View reference.
- Chen et al. Far infrared irradiation suppresses experimental arthritis in rats by down-regulation of genes involved inflammatory response and autoimmunity. J Adv Res. 2022;38:107-118. PMID:35572409.
- Hojo T, Fujioka M, Otsuka G, et al. Effect of heat stimulation on viability and proteoglycan metabolism of cultured chondrocytes: preliminary report. J Orthop Sci. 2003;8:396-399. View reference.
- Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee. Arthritis Care Res. 2020;72(2):149-162. View reference.
- Lehmann JF, Masock AJ, Warren CG, Koblanski JN. Effect of therapeutic temperatures on tendon extensibility. Arch Phys Med Rehabil. 1970;51(8):481-487.
- Oosterveld FGJ, Rasker JJ, Floors M, et al. 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. Clin Rheumatol. 2009;28(1):29-34. View reference.
- Park JH, Lee S, Cho DH, Park YM, Kang DH, Jo I. Far-infrared radiation acutely increases nitric oxide production by increasing Ca²⁺ mobilization and Ca²⁺/calmodulin-dependent protein kinase II-mediated phosphorylation of endothelial nitric oxide synthase at serine 1179. Biochem Biophys Res Commun. 2013;436(4):601-606. PMID:23756809.
- Qin B, Lu HA, Xu XF, et al. Alleviation of osteoarthritis progression through far-infrared therapy targeting osteoclast cytoskeleton and MAPK/c-Fos/NFATc1 signaling inhibition. Pharmacol Res. 2026;228:108221. View reference.
- Tsagkaris C, Papazoglou AS, Eleftheriades A, et al. Infrared radiation in the management of musculoskeletal conditions and chronic pain: a systematic review. Eur J Investig Health Psychol Educ. 2022;12(3):334-343. View reference.
