“Sauna lowers inflammation in your body.”

The research found this

The claim comes from the Finnish KIHD cohort. In 2,084 men without inflammatory disease, average CRP was 2.41 in weekly bathers and 1.65 in men who went four to seven times a week.1Source 1 · Cross-sectional studySauna bathing and systemic inflammationLaukkanen JA, Laukkanen T. European Journal of Epidemiology, 2018.Read the paper ↗PubMed ↗ The letter printed the unit as mmol/L, where CRP is normally reported in mg/L.

A second analysis of the same men took account of age, body mass index, smoking, physical activity and other factors. CRP was 0.84 mg/L lower in the four-to-seven group than in weekly bathers at baseline and 1.66 mg/L lower 11 years later, although sauna frequency and CRP correlated only weakly (r = −0.07).2Source 2 · Cohort studyLongitudinal associations of sauna bathing with inflammation and oxidative stress: the KIHD prospective cohort studyKunutsor SK, Laukkanen T, Laukkanen JA. Annals of Medicine, 2018.Read the paper ↗PubMed ↗

The heating trials found no change. A 2025 meta-analysis of 51 controlled studies found CRP unchanged after single or repeated sessions, and a pooled analysis of 20 randomized trials of at least a week of heating found no effect on CRP.3Source 3 · Meta-analysisHeat thermotherapy to improve cardiovascular function and cardiometabolic health: A systematic review and meta‐analysisPrice BS, Lucas SJE, Akerman AP, et al.. Experimental Physiology, 2025.Read the paper ↗PubMed ↗4Source 4 · Meta-analysisNon-acute effects of passive heating interventions on cardiometabolic risk and vascular health: systematic review and meta-analysis of randomized controlled trialsHamaya R, Joyama Y, Miyata T, et al.. American Journal of Preventive Cardiology, 2025.Read the paper ↗PubMed ↗ Four weeks of 30-minute saunas after cycling left CRP unchanged in a small randomized trial of 15 men.5Source 5 · Randomized trialNo effects of a 4-week post-exercise sauna bathing on targeted gut microbiota and intestinal barrier function, and hsCRP in healthy men: a pilot randomized controlled trialKarolkiewicz J, Nieman DC, Cisoń T, et al.. BMC Sports Science, Medicine and Rehabilitation, 2022.Read the paper ↗PubMed ↗

A single session nudges some inflammatory signals up. Two 10-minute rounds at 80°C raised IL-6 by 0.92 pg/mL about an hour later in adults averaging 66, while a single round did not. CRP stayed flat after both.6Source 6 · Crossover trialImpact of Finnish sauna bathing on circulating markers of inflammation in healthy middle-aged and older adults: A crossover studyBehzadi P, Gravel H, Neagoe PE, et al.. Complementary Therapies in Medicine, 2020.Read the paper ↗PubMed ↗ In a head-to-head test only hot water raised IL-6, and whole-body hyperthermia for depression tripled it.7Source 7 · Crossover trialComparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalitiesAtencio JK, Reed EL, Wiedenfeld Needham K, et al.. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2025.Read the paper ↗PubMed ↗8Source 8 · Clinical trialThe antidepressant effect of whole-body hyperthermia is associated with the classical interleukin-6 signaling pathwayMac Giollabhui N, Lowry CA, Nyer M, et al.. Brain, Behavior, and Immunity, 2024.Read the paper ↗PubMed ↗ After a 30-minute sauna, only 2 of 37 cytokines changed, and both fell.9Source 9 · Clinical trialAcute Finnish sauna heat exposure induces stronger immune cell than cytokine responsesHeinonen IH, Koivula T, Hollmén M, et al.. Temperature, 2026.Read the paper ↗PubMed ↗

One small trial in heart failure reported lower CRP and other inflammatory markers after two weeks of daily 10-minute hot-spring baths at 40°C.10Source 10 · Randomized trialHyperthermia by bathing in a hot spring improves cardiovascular functions and reduces the production of inflammatory cytokines in patients with chronic heart failureOyama JI, Kudo Y, Maeda T, et al.. Heart and Vessels, 2013.Read the paper ↗PubMed ↗