Did you know that since 1957 sauna therapy has been used as a potential way to prevent the flu?  It’s true! During World War II, sauna therapy was even noted to prevent the spread of typhus fever in Finnish troops, “The main method of typhus prevention in Finland consisted of regular sauna bathing, which was culturally acceptable and very efficient.”  Since then, numerous studies have been published confirming that sauna therapy is indeed beneficial for fighting infections.[3,4]
For example, a clinical study divided 50 patients into two groups, one group of patients were assigned to sauna sessions over several months and the other group did not receive sauna therapy; can you guess what happened? The group that received sauna sessions had their incidence of the common cold cut in half.  And the benefits of sauna therapy don’t stop at the common cold. People who use saunas at least 4 times per week, compared to those who use the sauna once per week or less, have approximately half the risk of developing pneumonia or respiratory diseases. [5,6]
So how does going into a sauna help fight against infections? For one, our body’s first defense against infection is a fever. By boosting core body temperature, and mimicking a fever, sauna therapy may help our bodies fight off infections before they take hold. It’s not recommended to go into a sauna once you have a fever because at that point your body is doing sauna therapy on its own. However, the consistent use of a sauna may help reduce the ability of viruses to replicate in the body. [4-6] And this is important, especially early on in an infection, prior to it causing a fever, spreading to the lungs and taking a firm hold.
Going into the sauna causes hyperthermia or a rise in core body temperature. Essentially, sauna therapy is “heat shock” therapy. It shocks the body with heat and induces a short-term stress on the body. However, once the body has recovered from a sauna session it is more resilient to other stressors. This is known as hormesis. Basically, what doesn’t kill you makes you stronger (think of sunlight, exercise, or cold therapy). And in the case of sauna therapy we are talking about the immune system getting stronger.
We didn’t know exactly how saunas worked against viruses until recently. For example, when we go into a sauna our body increases the production of something called heat shock proteins (HSPs).  HSPs are released to prevent proteins from degenerating from heat shock or other stress.  They also help stimulate both our innate and adaptive immune system.  Thus, making our overall immune system more robust. Additionally, heat shock proteins can directly inhibit influenza viral replication [10-12] and make our cells more resistant to death from external stressors. [13, 14] In other words, the release of heat shock proteins with sauna therapy may, 1.) boost our immune system, 2.) inhibit viral replication and 3.) protect our immune and lung cells during cytokine storms. Talk about a triple combination punch!
The benefits of HSPs and sauna therapy on our immune system don’t stop there. Heat shock protein-70 can stimulate the release of nitric oxide from monocytes.  And nitric oxide can inhibit the replication of severe acute respiratory syndrome (SARS). [16 , 17 , 18] Additionally, sauna therapy boosts nitric oxide,  as it increases the expression of endothelial nitric oxide synthase (eNOS), which is the enzyme that makes nitric oxide in the body. [20, 21] Infrared sauna therapy stimulates eNOS above and beyond any thermal effect, suggesting that infrared saunas may have an advantage over traditional saunas.[20, 22, 23]
A 15-minute sauna session can also stimulate the immune system, increasing the number of white blood cells, lymphocytes, neutrophils and basophil counts.  Hyperthermia, as found with sauna therapy, also increases the antiviral effect of interferons. [25 , 26] Interferons are produced by our body to increase antiviral antibodies and to stimulate our immune system. Thus, there are many pathways for how sauna therapy may help us fight against infections.
Overall, sitting in a sauna for approximately 15-30 minutes per day, for 4 or more days per week, is a great way to increase heat shock proteins, activate the immune system and potentially inhibit viral replication. Clinical evidence in humans suggests that sauna therapy reduces the incidence of the common cold and may reduce the incidence of influenza, pneumonia and respiratory diseases.
- Hartmann A. [Asiatic flu in 1957; sauna baths as prophylactic measure]. Hippokrates 1958;29:153-4.
- Laurent H. Control of typhus fever in Finland during World War II. Vesalius 2009;15:71-9.
- Brenke R. Das Potenzial der Sauna im Rahmen der Prävention – eine Übersicht neuerer Erkenntnisse. Forschende Komplementarmedizin (2006) 2015;22:320-5.
- Ernst E, Pecho E, Wirz P, et al. Regular sauna bathing and the incidence of common colds. Ann Med 1990;22:225-7.
- Kunutsor SK, Laukkanen T, Laukkanen JA. Frequent sauna bathing may reduce the risk of pneumonia in middle-aged Caucasian men: The KIHD prospective cohort study. Respir Med 2017;132:161-3.
- Kunutsor SK, Laukkanen T, Laukkanen JA. Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. Eur J Epidemiol 2017;32:1107-11.
- Iguchi M, Littmann AE, Chang SH, et al. Heat stress and cardiovascular, hormonal, and
heat shock proteins in humans. Journal of athletic training 2012;47:184-90.
- Xue J, Fan X, Yu J, et al. Short-Term Heat Shock Affects Host-Virus Interaction in Mice Infected with Highly Pathogenic Avian Influenza Virus H5N1. Frontiers in microbiology 2016;7:924.
- Wang Y, Whittall T, McGowan E, et al. Identification of stimulating and inhibitory epitopes within the heat shock protein 70 molecule that modulate cytokine production and maturation of dendritic cells. J Immunol 2005;174:3306-16.
- Hirayama E, Atagi H, Hiraki A, et al. Heat shock protein 70 is related to thermal inhibition of nuclear export of the influenza virus ribonucleoprotein complex. J Virol 2004;78:1263-70.
- Li G, Zhang J, Tong X, et al. Heat shock protein 70 inhibits the activity of Influenza A virus ribonucleoprotein and blocks the replication of virus in vitro and in vivo. PLoS One 2011;6:e16546.
- Conti C, De Marco A, Mastromarino P, et al. Antiviral effect of hyperthermic treatment in rhinovirus infection. Antimicrob Agents Chemother 1999;43:822-9.
- Novoselova TV, Margulis BA, Novoselov SS, et al. Treatment with extracellular HSP70/HSC70 protein can reduce polyglutamine toxicity and aggregation. J Neurochem 2005;94:597-606.
- Guzhova IV, Arnholdt AC, Darieva ZA, et al. Effects of exogenous stress protein 70 on the functional properties of human promonocytes through binding to cell surface and internalization. Cell Stress Chaperones 1998;3:67-77.
- Wang Y, Kelly CG, Singh M, et al. Stimulation of Th1-polarizing cytokines, C-C chemokines, maturation of dendritic cells, and adjuvant function by the peptide binding fragment of heat shock protein 70. J Immunol 2002;169:2422-9.
- Akerstrom S, Mousavi-Jazi M, Klingstrom J, et al. Nitric oxide inhibits the replication cycle of severe acute respiratory syndrome coronavirus. J Virol 2005;79:1966-9.
- Akerstrom S, Gunalan V, Keng CT, et al. Dual effect of nitric oxide on SARS-CoV replication: viral RNA production and palmitoylation of the S protein are affected. Virology 2009;395:1-9.
- Chen L, Liu P, Gao H, et al. Inhalation of nitric oxide in the treatment of severe acute respiratory syndrome: a rescue trial in Beijing. Clin Infect Dis 2004;39:1531-5.
- Gryka D, Pilch WB, Czerwinska-Ledwig OM, et al. The influence of Finnish sauna treatments on the concentrations of nitric oxide, 3-nitrotyrosine and selected markers of oxidative status in training and non-training men. Int J Occup Med Environ Health 2020;33:173-
- Huang PH, Chen JW, Lin CP, et al. Far infra-red therapy promotes ischemia-induced angiogenesis in diabetic mice and restores high glucose-suppressed endothelial progenitor cell functions. Cardiovasc Diabetol 2012;11:99.
- Ikeda Y, Biro S, Kamogawa Y, et al. Repeated sauna therapy increases arterial endothelial nitric oxide synthase expression and nitric oxide production in cardiomyopathic hamsters. Circ J 2005;69:722-9.
- Akasaki Y, Miyata M, Eto H, et al. Repeated thermal therapy up-regulates endothelial nitric oxide synthase and augments angiogenesis in a mouse model of hindlimb ischemia. Circ J 2006;70:463-70.
- Yu SY, Chiu JH, Yang SD, et al. Biological effect of far-infrared therapy on increasing skin microcirculation in rats. Photodermatol Photoimmunol Photomed 2006;22:78-86.
- Pilch W, Pokora I, Szygula Z, et al. Effect of a single finnish sauna session on white blood cell profile and cortisol levels in athletes and non-athletes. Journal of human kinetics 2013;39:127-35.
- Chang CC, Wu JM. Modulation of antiviral activity of interferon and 2',5'-oligoadenylate synthetase gene expression by mild hyperthermia (39.5 degrees C) in cultured human cells. J Biol Chem 1991;266:4605-12.
- Payne J, Nair MP, Ambrus JL, et al. Mild hyperthermia modulates biological activities of interferons. Int J Hyperthermia 2000;16:492-507.