Why hydrotherapy might work in COVID-19

Coronaviruses don’t like the heat. In fact at 38 deg C they have a massive drop in replication and infectivity. [1]  In the lab they are grown at 34 deg C. [2]

Coronaviruses inhibit the innate immune system: the first line of the body’s defence against viruses.  In particular they directly impair the release of the “distress beacon” cells send out to say they are infected (Interferon Type 1 “IFN Type 1”) and (either consequently or directly) inhibit the cell lines (eg monocytes and natural killer cells) in the innate immune system. [3,4] These messages and cells are essential to switch on a normal, healthy, adaptive immune response rather than the late, overactive and damaging immune response seen in hospitalised patients with COVID-19.

Cold temperatures impair the immune system’s ability to release IFN Type 1 when infected with a virus (in mice). [5]

So being cold both improves the growth of coronaviruses and impairs the body’s distress signal to show it is under attack, which is already being directly inhibited by the coronavirus.

Older people, and those with obesity (with or without the diseases associated with carrying extra weight) have impaired innate and adaptive immune systems, including a decreased ability to mount a fever to an infection. They also have decreased numbers and activity of cells such as natural killer cells and monocyte function [6-8].

So older and unwell/obese people are hit doubly hard by their own weakened innate immune response and the active attack of that area of the immune system by the virus that causes COVID-19.

Fever is a broad based stimulant to the whole of the innate and adaptive immune system [9].   In particular, in respect to COVID-19 infection, fever or hyperthermia increases the release of INF Type 1 and monocyte function [10-12] and directly inhibits viral replication [9]. There are similar results to the immune system if the body temperature is raised by external means eg sitting in a hot bath, as by internal means such as infection [9].

So inducing mild hyperthermia by water (also known as “hydrotherapy”) could directly

  • inhibit replication and activity of coronaviruses
  • overcome coronavirus inhibition of IFN Type 1, likely increasing the chances of normal immune resolution of COVID-19
  • Enhance immune function in those most vulnerable to immune complications of COVID-19

Hydrotherapy was used widely in Adventist hospitals in the Spanish Influenza pandemic with a mortality rate of 1% compared to 13% in the army-run “open air” hospitals considered state of the art at the time. Average mortality was 40% for hospitalised patients in traditional hospitals [13-15]. (NB these are old figures and not subject to the academic standards of research and trials of today. Nonetheless they are interesting to note.)

Hydrotherapeutic treatments have received little study since the advent of vaccination and effective antibiotic therapy.  Consequently there are no randomised controlled trials to support their use in coronaviruses of any sort, let alone COVID-19, but for the above reasons it is plausible to think it should be useful.   Early preparations are underway for a trial in Australia. In other cities around the world there is more urgency. 

It makes sense to use the time at home after diagnosis of COVID-19 to support the immune system to clear the virus, and increase the chance of a good resolution.  It feels like a better  alternative than to just cross your fingers and hope you are not one of the 20% who need to go to hospital, 5% who need ICU or 2.5% who do not survive.  There are multiple drugs and immunotherapies being trialled but most of these are being focused on the late stages of the illness and are not readily available now.  Besides hydrotherapy it makes sense to eat nutritious food, get enough rest, and manage stress. Quitting smoking and limiting your alcohol intake (if you do drink) are also great ideas for this time.

Hydrotherapy is a medical treatment like any other with risks and benefits. Please read the advice about contraindications and safety precautions carefully, and DO NOT USE HYDROTHERAPY INSTEAD OF APPROPRIATE MEDICAL CARE.  You should use the treatments outlined on this website only with the support of your local doctor, who can help you determine if it is safe for you, or help you modify them to make them safer for you.

(Written 10/04/20 by Dr Emma Campbell, BMed FRACGP)


(If you have little time, focus on numbers four and nine).

  1. Chan KH, Peiris JS, Lam SY, Poon LL, Yuen KY, Seto WH. The Effects of Temperature and Relative Humidity on the Viability of the SARS Coronavirus. Adv Virol. 2011;2011:734690. doi: 10.1155/2011/734690. Epub 2011 Oct 1. PubMed PMID: 22312351; PubMed Central PMCID: PMC3265313.
  2. 2.Kaye M. SARS-associated coronavirus replication in cell lines. Emerg Infect Dis. 2006 Jan;12(1):128-33. doi: 10.3201/eid1201.050496. PubMed PMID: 16494729; PubMed Central PMCID: 
  3. R, Fehr AR, Zheng J, Wohlford-Lenane C, Abrahante JE, Mack M, Sompallae R, McCray PB Jr, Meyerholz DK, Perlman S. IFN-I response timing relative to virus replication determines MERS coronavirus infection outcomes. J Clin Invest. 2019 Jul 29;130:3625-3639. doi: 10.1172/JCI126363. eCollection 2019 Jul 29. PubMed PMID: 31355779; PubMed Central PMCID: PMC6715373.
  4. Prompetchara E, Ketloy C, Palaga T. Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic. Asian Pac J Allergy Immunol. 2020 Mar;38(1):1-9. doi: 10.12932/AP-200220-0772. Review. PubMed PMID: 32105090.
  5. Prow NA, Tang B, Gardner J, Le TT, Taylor A, Poo YS, Nakayama E, Hirata TDC, Nakaya HI, Slonchak A, Mukhopadhyay P, Mahalingam S, Schroder WA, Klimstra W, Suhrbier A. Lower temperatures reduce type I interferon activity and promote alphaviral arthritis. PLoS Pathog. 2017 Dec;13(12):e1006788. Doi:
  6. Poland GA, Ovsyannikova IG, Kennedy RB, Lambert ND, Kirkland JL. A systems biology approach to the effect of aging, immunosenescence and vaccine response. Curr Opin Immunol. 2014 Aug;29:62-8. doi: 10.1016/j.coi.2014.04.005. Epub 2014 May 13. Review. PubMed PMID: 24820347; PubMed Central PMCID: PMC4119552
  7. Rao DV, Watson K, Jones GL. Age-related attenuation in the expression of the major heat shock proteins in human peripheral lymphocytes. Mech Ageing Dev. 1999 Feb 1;107(1):105-18. doi: 10.1016/s0047-6374(98)00143-2. PubMed PMID: 10197792.
  8. Parisi MM, Grun LK, Lavandoski P, Alves LB, Bristot IJ, Mattiello R, Mottin CC, Klamt F, Jones MH, Padoin AV, Guma FCR, Barbé-Tuana FM. Immunosenescence Induced by Plasma from Individuals with Obesity Caused Cell Signaling Dysfunction and Inflammation. Obesity (Silver Spring). 2017 Sep;25(9):1523-1531. doi: 10.1002/oby.21888. Epub 2017 Jul 14. PubMed PMID: 28707376
  9. Evans SS, Repasky EA, Fisher DT. Fever and the thermal regulation of immunity: the immune system feels the heat. Nat Rev Immunol. 2015 Jun;15(6):335-49. doi: 10.1038/nri3843. Epub 2015 May 15. Review. PubMed PMID: 25976513; PubMed Central PMCID: PMC4786079
  10. Postic B, DeAngelis C, Breinig MK, Monto HO. Effect of temperature on the induction of interferons by endotoxin and virus. J Bacteriol. 1966 Mar;91(3):1277-81. PubMed PMID: 5929756; PubMed Central PMCID: PMC316024.
  11. Manzella JP, Roberts NJ Jr. Human macrophage and lymphocyte responses to mitogen stimulation after exposure to influenza virus, ascorbic acid, and hyperthermia. J Immunol. 1979 Nov;123(5):1940-4. PubMed PMID: 489966.
  12. Knippertz I, Stein MF, Dörrie J, Schaft N, Müller I, Deinzer A, Steinkasserer A, Nettelbeck DM. Mild hyperthermia enhances human monocyte-derived dendritic cell functions and offers potential for applications in vaccination strategies. Int J  Hyperthermia. 2011;27(6):591-603. doi: 10.3109/02656736.2011.589234. PubMed PMID: 21846195.
  13. Hobday RA, Cason JW. The open-air treatment of pandemic influenza. Am J Public Health. 2009 Oct;99 Suppl 2:S236-42. doi: 10.2105/AJPH.2008.134627. Epub 2009 May 21. PubMed PMID: 19461112; PubMed Central PMCID: PMC4504358.
  14. WEAPONS AGAINST INFLUENZA. Am J Public Health (N Y). 1918 Oct;8(10):787-8. doi: 10.2105/ajph.8.10.787. PMID: 18009972; PMCID: PMC1362349
  15. W.A. Ruble, MD, Sanitarium Treatment of Influenza, Life & Health, 34 (5);114-115. May 1919. Graphics: Applied Physiology Lab WLCH ’09. BEB ibid.Accessed at: https://adventistdigitallibrary.org/adl-373944/life-and-health-may-1-1919 pg 20