Viruses that are contained within a lipid membrane or “enveloped viruses” such as coronaviruses and rhinoviruses can remain active for long periods in cool, dry conditions, which can lead to increased rates of respiratory infections.
However, these viruses, which include severe acute respiratory syndrome coronavirus (SARS-CoV-2) are sensitive to heat, and temperatures tolerable to humans, can be enough to destroy the lipid envelope and deactivate them.
Novel Coronavirus SARS-CoV-2 Transmission electron micrograph of SARS-CoV-2 virus particles, isolated from a patient. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
All mammals use fever as a way to manage infection, and historically, heat has been used in the form of hot springs, saunas, hot mud and sweat-lodges to treat and prevent respiratory tract infections.
The relatively low cost, convenience, and ease of access to heat-based therapy, along with its multiple physical and psychological beneficial effects, make this type of therapy a desirable option for helping to fight respiratory infections.
Heat is also often used to deactivate the viruses included in vaccines, with temperatures of 55 to 65°C having been shown to inactivate various types of enveloped viruses, including coronaviruses.
However, no clinical protocols are currently in place for the use of heat treatments in cases of coronavirus disease 2019 (COVID-19), as heat has not yet been proved effective as a means of treatment or prevention.
Now, Dr. Mark Cohen, Founder of the Extreme Wellness Institute* in Melbourne, Australia, has reviewed some of the evidence supporting the use of heat in the treatment and prevention of viral infections, as well as some of the proposed underlying physiological and psychological mechanisms of action.
The first line of defense following viral infection
One of the first lines of defense during the initial phase of respiratory viral infection is the upper airways, which provide a mucosal barrier that traps virions and enables them to be recognized by the immune system. Virions are also moved by the mucocilia towards the throat, where they can be swallowed or expelled from the body through coughing or sneezing.
Cohen says the ability of cool, dry conditions to enhance viral infection has been demonstrated in a study of mice. Compared with a humidity of 50%, a humidity of around 20% slowed mucociliary clearance in the animals, impaired their innate antiviral defense mechanisms, and reduced tissue repair, leading to more severe illness.
During the initial phase of a viral infection, the inhalation of hot, humid air can support the immune system’s first line of defense, by directly inhibiting or deactivating virions lodged in the upper airway and by aiding mucociliary clearance.
This can also be further enhanced by inhaling steam, says Cohen.
Writing on the Open Research publishing platform F1000Research, Cohen says, “the inhalation of steam with added essential oils with antiviral, decongestant, anxiolytic and other properties, may further assist in facilitating mucociliary clearance and reducing viral load as well as providing physical and psychological relief.”
The second line of defense
Next, Cohen talks about the body’s second line of defense, saying that if respiratory viruses manage to survive the first line of defense, they will then encounter the effects of fever, which is part of the body’s acute phase response.
Heat applied to the whole body mimics fever, thereby enhancing this second line of defense and activating multiple cellular responses regulated by the immune system, inflammation, and the heat shock response pathway.
Febrile temperatures have been demonstrated to make the membranes of immune cells more fluid, which increases their proliferation and the effectiveness of their response to viral threats.
The psychological benefits of heat-treatment
Cohen also discusses the psychological benefits heat-based treatments provide by helping people focus, relax, and sleep. In the context of lockdown measures, sauna bathing, for example, can divert attention from stress-inducing media reports and relieve the boredom that can manifest as a result of self-isolation. Sauna bathing has also been shown to enhance sleep, which in turn, supports immune function.
The challenges faced
Although there is evidence to support the use of heat-based treatments for the prevention and treatment of viral respiratory infections, no clinical protocols currently exist that are relevant to COVID-19. Nevertheless, a long history of traditional use and a wide range of traditional practices could help to inform their development, says Cohen.
However, implementing heat-based therapies would be challenging, he adds: “The current pandemic has seen the fear of infection lead to the widespread closure of public facilities such as bathing facilities, commercial hot springs, spas, gymnasiums, hotels and fitness centers that offer saunas and heat treatments.”
On the other hand, some moves are in place to start re-opening facilities as quarantined areas where people can receive heat treatments and where medical staff can relax. It may also be possible to incorporate saunas and steam rooms within hospital buildings and rehabilitation centers for both staff and patients to use. In addition, simple, home-based protocols would provide isolated or quarantined individuals with guidance about using heat-based treatments.
Crowdsourced, citizen-science platforms could help optimize strategies
Cohen suggests that such protocols could be assessed using crowdsourced, citizen-science platforms, which could help to develop, test, and optimize heat-treatment strategies for current and future pandemics.
“While there are significant challenges in implementing heat-based therapies during the current pandemic,” he writes… “these therapies present an opportunity to integrate natural medicine, conventional medicine and traditional wellness practices, and support the wellbeing of both patients and medical staff, while building community resilience and reducing the likelihood and impact of future pandemics.”
Dr. Marc Cohen is a medical doctor who is a Board Member of the Global Wellness Summit and a shareholder in Maruia Hot Springs, which is a boutique hot springs resort in the Southern Alps of New Zealand. He is also a Member of the Global Thermal Think Tank, Co-Founder of the Bathe the World Foundation and Founder of the Extreme Wellness Institute.