“Sauna relieves chronic pain and arthritis.”

The research found this

Waon therapy is a Japanese protocol: 15 minutes in a 60°C far-infrared sauna, then 30 minutes under a blanket. In 13 women with fibromyalgia who had it two or five days a week, pain fell 11% to 70% after the first session and 20% to 78% after 10 treatments, and it stayed lower through the observation period.1Source 1 · Case seriesEfficacy of Waon Therapy for FibromyalgiaMatsushita K, Masuda A, Tei C. Internal Medicine, 2008.Read the paper ↗PubMed ↗ The study had no control group.

In 46 inpatients with chronic pain, 22 had daily far-infrared sauna and warming added to a four-week multidisciplinary program and 24 had the program alone. Pain fell in both groups, and only anger scores ended lower with sauna.2Source 2 · Clinical trialThe Effects of Repeated Thermal Therapy for Patients with Chronic PainMasuda A, Koga Y, Hattanmaru M, et al.. Psychotherapy and Psychosomatics, 2005.Read the paper ↗PubMed ↗ Two years later, 77% of the sauna group had returned to work against 50% of the others. The abstract does not say how patients were assigned.

For arthritis there is one pilot. Seventeen people with rheumatoid arthritis and 17 with ankylosing spondylitis took eight infrared sauna sessions over four weeks. Pain and stiffness fell during sessions and fatigue eased. Over the four weeks the improvements fell short of statistical significance, and disease activity did not change. No one had a flare.3Source 3 · Clinical trialInfrared sauna in patients with rheumatoid arthritis and ankylosing spondylitisOosterveld FGJ, Rasker JJ, Floors M, et al.. Clinical Rheumatology, 2009.Read the paper ↗PubMed ↗

The one clearly randomized trial is in headache. Thirty-seven people with chronic tension-type headache got advice alone or advice plus regular sauna for eight weeks, and headache intensity came out 1.27 points lower with sauna on a numerical pain scale.4Source 4 · Randomized trialEfficacy of Regular Sauna Bathing for Chronic Tension-Type Headache: A Randomized Controlled StudyKanji G, Weatherall M, Peter R, et al.. The Journal of Alternative and Complementary Medicine, 2015.Read the paper ↗PubMed ↗ Duration, sleep, depression and disability did not differ.

After hard training, 20 minutes of infrared sauna at 43°C left 16 basketball players with less soreness and a smaller drop in jump height 14 hours later than passive rest did.5Source 5 · Crossover trialA post-exercise infrared sauna session improves recovery of neuromuscular performance and muscle soreness after resistance exercise trainingAhokas EK, Ihalainen J, Hanstock HG, et al.. Biology of Sport, 2023.Read the paper ↗PubMed ↗ Soreness was self-rated, and the players knew which session they had.