Turning up the heat on COVID-19: Heat as a therapeutic intervention

This text is a translation and summary of an elaboration by Dr. Marc Cohen. The full article and more information about the author can be found here.

Below we will discuss the use of heat to treat and prevent viral infections:

People develop fevers to fight infections in the body. This is because viruses – particularly those with viral envelopes, such as SARS-COV-2 – are sensitive to heat. They are destroyed at temperatures that are still well tolerable for humans.

For as long as humans have existed, they have used heat in the form of hot springs, saunas, hammams, steam baths, sweat huts, steam inhalations, hot mud and compresses to prevent and treat respiratory infections and improve health and well-being.

Especially in the early stages of an infection, inhaled heat can support the immune system. This is because the heat acts on the upper respiratory tract. In addition, heat applied to the whole body also supports the immune system by mimicking fever and activating innate and acquired immune defenses and building physiological resistance. Psychologically, heat treatment is also beneficial because it directs focus to positive action, improves relaxation and sleep. Heat is a cheap, convenient, and widely accessible therapeutic intervention. And although there are no clinical protocols for the use of heat to treat COVID-19, protocols based on traditional practices that consider contraindications, adverse effects, and infection control measures could be developed and widely implemented quickly and cost-effectively.

Although there are significant challenges to implementing heat-based therapies during the current pandemic, these therapies represent an opportunity to integrate natural medicine, conventional medicine, and traditional wellness practices to support the well-being of patients and healthcare professionals while building community resilience and reducing the likelihood and impact of future pandemics.

Warmth in viruses and mammals

Life exists within a narrowly defined temperature range, but viruses, which are technically not alive, can remain biologically active in a wide range of environments.
Enveloped viruses, such as rhinoviruses or coronaviruses, are most active in cool, dry conditions associated with increased incidence of respiratory infections (1), including infections with SARS-CoV (2) and SARS-CoV-2 (3). However, the lipid envelope is destroyed at warmer temperatures – still tolerable for humans. Exactly, heat 55 to 65 °C for 15 to 30 minutes is reported to deactivate a number of enveloped viruses, including coronaviruses (4).
The first line of defense against respiratory viruses is the nasal cavity and sinuses, which maintain a protective mucosal barrier that allows viruses to be intercepted, identified by the immune system, and then flushed away.
In winter, when sunlight is limited and the air is cold and dry, the nasal cavity becomes the coldest part of the body, and as the airways dry out and mucus becomes thicker and more difficult to clear, conditions become more favorable for virus invasion and replication.
When respiratory viruses overcome the first line of defense – the nasal cavity and sinuses – fever is produced as part of the acute phase response. This is the second line of defense of the immune system.


Mechanisms of action

Whether internally generated or externally applied, heat has a profound effect on host defenses and physiological resistance. The mechanisms by which heat overcomes viral infections depend on the setting, source, temperature, humidity, location, and timing of the applied heat.
Inhalation of hot air can support the immune system’s first line of defense by directly inhibiting or deactivating virions [single viral particle located outside a cell d.ed.] in the upper respiratory tract where they first attach, which can be enhanced by inhalation of steam (5). Heat applied to the whole body further supports the immune system’s second line of defense by developing heat stress that mimics the effects of fever (6).
In addition to enhancing cellular responses, heat stress increases cardiac output, plasma volume, and peripheral blood flow, and induces detoxification through the liver and kidneys and through the skin via sweating (7), preferentially eliminating some toxic elements (8). Heat stress also elicits a hormonal stress response that builds physiological resilience and confers tolerance to subsequent stress, similar to exercise (9).
Heat stress may provide another benefit against viral respiratory infections by altering blood pH. Hyperthermia induces hyperventilation and subsequent respiratory alkalosis (10), which creates alkaline conditions that may be more favorable for host defense. The ability of a transient alkaline environment to inhibit viral replication and reduce infectivity has been demonstrated. (11)(12)
In addition to the physiological benefits of fighting viral infections such as COVID-19, heat also provides many psychological benefits. Sauna bathing and other forms of heat therapy require time and effort for active relaxation, which can help divert attention from anxiety-provoking messages and/or relieve the boredom associated with social confinement. Sauna bathing also improves sleep, which in turn supports immune function. Engaging in an activity with an intended positive outcome can also provide a sense of control that might otherwise be lacking, and doing something that feels good and having positive expectations evokes the power of positive thoughts and the placebo effect or “remembered well-being” (13). In a time of distance, saunas can also provide an opportunity for close family members to come together in a way that has supported family cohesion in Finland and other Nordic countries for generations (14).


Heat as medicine

Hot springs, saunas, hammams, steam baths, sweat lodges, steam inhalations, baths, hot mud, and poultices have traditionally been used in cold, dry climates to prevent and treat respiratory infections and improve overall health and well-being. While heat-based therapies are not widely used in conventional medicine, aside from the local application of hot packs to relieve symptoms, heat-based treatments are standard offerings in wellness facilities, such as hot springs, bathing facilities, gyms, fitness centers, hotels, and resorts, where they are used as both therapy and recreation (15).
There are several lines of evidence supporting the use of heat and humidity to prevent and treat viral respiratory infections. Historical and emerging evidence suggests that regular sauna bathing improves cardiovascular, respiratory, and immunologic function and enhances mood and quality of life (16). Epidemiologic evidence also suggests that frequent sauna bathing is associated with a reduced risk of pneumonia and viral infections (17), and randomized controlled trials suggest that regular sauna bathing may halve the incidence of respiratory viral infections (18). Randomized controlled trials also suggest that hot air can treat respiratory infections, with humidified air at temperatures above 43°C for 20 to 30 minutes found to reduce the spread, provide immediate symptom relief, and improve the course of a cold (19).


Clinical applications and implications

There are a number of heat-based interventions that can be used, in addition to spacing, hand washing, and other personal hygiene measures, to help overcome COVID-19. For example, indoor heating and humidification can prevent drying of the nasal mucosa and increase nasal patency and provide symptomatic relief (20). Direct application of heat to the upper respiratory tract at the first signs of infection may also serve to inhibit or deactivate virions at the site where they first colonize. Inhalation of steam with added essential oils, which have antiviral, decongestant, anxiolytic, and other properties, may further help reduce viral load and provide physical and psychological relief (21).
There are currently no clinical treatment protocols for the use of heat to treat COVID-19; however, heat has a long history of traditional use, and conventional practices such as alternating hot and cold immersion baths, relaxation after heat treatment, and the use of essential oils may influence its development. Heat-based clinical protocols need to consider temperature, timing, and individual tolerance, as well as humidity. There are no clinical studies on this yet, but efforts should be made in a timely manner, taking into account contraindications.
Although the clinical application of heat in the prevention and treatment of COVID-19 is promising, there are significant challenges in implementing heat-based therapies. The current pandemic has resulted in fear of contagion leading to widespread closure of public facilities that offer saunas and heat treatments, such as bathing facilities, community hot springs, spas, gyms, hotels, and fitness centers, and while there are a large number of private saunas in some countries, such as Finland, private sauna ownership is limited to people of high socioeconomic status in most other places. Thus, if sauna bathing is to be widely adopted, public bathing and sauna facilities will need to adopt infection control measures similar to those used to manage COVID-19 in hospitals and medical facilities (22).



Heat is a cheap, convenient, and widely available therapeutic intervention with a long history of traditional use. It remains to be seen whether heat can be effective in the treatment or prevention of COVID-19. The relatively low cost and widespread availability of heat treatments, along with multiple mechanisms of action that include both physical and psychological aspects, make heat an attractive option for combating viral infections. Combining these ancient forms of treatment with modern technology can lead to greater integration of natural therapies into mainstream healthcare, with the potential to support the well-being of both patients and healthcare professionals. This may also lead to greater convergence between the health and wellness industries and the development of systems and activities that build wellness and resilience in the broader community, thereby reducing the impact of future pandemics.

From: Cohen M. Turning up the heat on COVID-19: heat as a therapeutic intervention [version 2; peer review: 2 approved]. F1000Research 2020, 9:292 (https://doi.org/10.12688/f1000research.23299.2) 


Source information:

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  2. Chan et al., 2011
  3. Sajadi et al., 2020; Wang et al., 2020
  4. Darnell et al., 2004; Duan et al., 2003; Hu et al., 2011; Kampf et al., 2020; Lelie et al., 1987; WHO Report, 2003
  5. Gujrathi et al., 2016
  6. Schieber & Ayres, 2016
  7. Crinnion, 2011
  8. Genuis et al., 2011
  9. Gálvez et al., 2018
  10. Tsuji et al., 2016
  11. Lamarre & Talbot, 1989
  12. Sturman et al., 1990
  13. Benson & Friedman, 1996
  14. Mather & Kaups, 1963
  15. Clark-Kennedy & Cohen, 2017
  16. Hussain & Cohen, 2018
  17. Kunutsor et al., 2017
  18. Ernst et al., 1990
  19. Tyrrell, 1988; Tyrrell et al., 1989
  20. Ophir & Elad, 1987
  21. Ali et al., 2015; Lee et al., 2017