With the coldest days of the year yet to come, the flu and cold season continue to herald in new cases by the day. As you look for ways to improve your own immune system this winter remember that turning to the heat of sauna therapy is a reliable means of improving overall resilience to viruses. The emphasis should be on ‘heat’ as relevant studies show that increasing the heat in your sauna does matter when it comes to improving overall immunity.
When you choose to use heat therapy to improve your immunity it is imperative that you ensure that your core temperature is rising and is dramatically affected by your sauna or even a hot bath. The key here is to artificially create a moderate fever to elicit the specific biological responses to enhance immunity as if a natural fever were occurring.
It is so easy to get lost in the literature surrounding sauna use and heat therapy in general. In addition to the numerous articles available, there are many short online videos that purport the utmost knowledge on the efficacy of certain styles of saunas over others. Scroll through social media and you will find hundreds of different opinions on what type of sauna to use, and exactly how to use it. Within the cacophony of entities grabbing your attention it is important to remember your own truth and reason for choosing to sauna, and if your reason is to enhance immunity during the winter months, then heat is your friend.
Different types of heat therapy offer varying health benefits, some of which overlap, and some of which are unique to specific heat therapy devices. So, if you know your principal reason for choosing to turn to heat therapy you can likely escape the maze of voices vying for your attention.
If your primary objective this winter is to boost your immunity then the rule of thumb is quite simple, get hot, and hotter! The new data shows that regardless of the mechanism of heat therapy that you choose to use, it is crucial that you are increasing your core temperature to a high enough degree to activate the biological responses necessary to provide the support for your immune system.
An Exploration of the Human Fever: How Does Thermoregulation Improve Immunity?
“An increase in core body temperature acts as an alert system to activate immune surveillance..” (1)
If you think about the last time you got really sick, what is the number one accompanying side effect? A fever, of course! Your body will naturally respond to an invasive virus by increasing your core temperature to help fight off outside invaders.
Whether you have a common cold, corona virus, or even a stomach ‘bug’,your body’s healing ability will increase the body’s temperature. Fevers ranging from close to a 100 degrees Fahrenheit, or to as high as 104 degrees are designed to elicit the immune system and engage your physiological mechanisms to win the battle against the intrusive virus.
The fever is a result of 600 million years of evolution according to the authors of the publication from the National LIbrary of Medicine entitled ‘Physiology, Fever’.
“The fever response is a systemic reaction to an infection that has evolved in warm-blooded animals for over 600 million years. An increase in core body temperature is known to improve survival and resolve infections.” (1)
The purpose of the fever is to ‘resolve infections’ by eliciting a response system from the body to activate against the outside threat. The authors from the same article describe this well.
“An increase in core body temperature acts as an alert system to activate immune surveillance via different cell types, including natural killer cells, dendritic cells, macrophages, T and B lymphocytes, neutrophils, and vascular endothelial cells.” (1)
If the purpose of a fever is to ring the alarm of the body’s alert system to activate aspects of the immune system into action, then can it be reasoned that if the body’s core temperature is increased artificially the same physiological responses would occur?
The answer is yes, by increasing the core temperature of the body by means other than a fever it is certainly possible to activate critical aspects of the immune system to ward off viruses before they become problematic.
The key to doing this is to ensure that the body is in fact increasing in core body temperature. This does not mean simply that the skin increases in temperature, or that the ambient air temperature is high, but that there is a measurable increase in the core temperature when using a thermometer for the body.
Here is a chart of fever grades:
- Low-grade: 37.3 to 38.0 C (99.1 to 100.4 F)
- Moderate-grade: 38.1 to 39.0 C (100.6 to 102.2 F)
- High-grade: 39.1 to 41 C (102.4 to 105.8 F)
- Hyperthermia: Greater than 41 C (105.8 F) (1)
When using any kind of heat therapy to pre-emptively improve immunity your goal should be to reach a moderate fever. If possible try to reach 101.5 degrees Fahrenheit ideally when you are in the sauna, and try to sustain this for 20 minutes to activate your immune response. (2)
It is not necessary or recommended to induce a high artificial fever, and it is certainly important to avoid the risk of heat stroke or Hyperthermia. Remember that when using any form of thermotherapy it is much more important to measure your personal temperature rather than the temperature of the air.
Upregulating Your Immune Response: A Comparison of Heat Therapy Modalities
If you would like to use a sauna or other heat therapy device to upregulate your immune response it is important to be able to recreate a moderate fever. To be clear, using a sauna in this fashion is what is needed to ameliorate immune function. It is possible to use saunas with other goals in mind other than the creation of an artificial fever for other purposes, but when it comes to immunity, high heat is the name of the game.
In a 2025 publication in the American Journal of Physiology entitled ‘Comparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalities’ (2) the use of three different styles of heat therapy were compared to find out what was necessary to induce the most effective immune response. This study compared hot baths, traditional hot air saunas, and infrared saunas.
There were an equal number of male and female participants in the study making a total of 20. Each participant took hot baths, traditional saunas, and infrared saunas. Blood was drawn before and after each 45 minute passive heat session. Heart rate, blood pressure, and water loss were all closely monitored. (2)
The participants used a hot water tub with a temperature of 40 degrees celcius for 45 minutes, three ten minute sessions of a traditional sauna set to 80 degrees celcius, and one 45 minute infrared sauna session to between 40-60 degrees celsius. (It is unclear why the temperature was set so low and variant for the infrared sauna).
In the cases where the participants were able to reach a moderate fever the results were astounding in favor of passive heat for the purposes of improving immunity. The primary biomarkers that appeared after an artificial fever was induced were an improvement in the presence of T cells, and T cell helpers. The authors write this with respect to the results.
“Secondary analyses of immune cell populations revealed a slight change in cytotoxic T cells, helper T cells, and natural killer cells.” (2)
Provided the participants were able to reach a moderate fever the results for enlisting the body’s immune response was very positive. The downside of this study is that participants were only able to reach an increase in core temperature during the hot water immersion. These results fly in the face of thousands of studies on sauna therapy using both traditional saunas, steam rooms, and infrared saunas.
The authors of this research consider why their study was unable to produce the same positive results for immunity during sauna use when compared to hot water use. It is clear that the hot water immersion method was conducted in a more thorough manner to ensure that a high internal body temperature was maintained.
The results from this study favored the hot water immersion method over either traditional sauna or infrared sauna to induce positive changes in immune response.
Here is a brief summary of what went wrong during the traditional sauna portion of this research. During the traditional sauna sessions too many breaks were given, whereas no breaks were given during the hot water immersion. This could be the reason why the traditional saunas were less effective at reaching a higher core temperature. Many studies are able to ensure that their participants reach the correct core temperature to elicit positive changes in the immune system, but the researchers of this paper likely provided too many opportunities for their participants to leave the sauna. Therefore a moderate fever was not reached.
The researchers made grave errors when using infrared saunas. The authors of the study do state that the size of the room used for the infrared sauna was much larger with less heating panels than is recommended so they were unable to maintain a high enough temperature. The authors of this research admit their own shortcomings when it came to using an appropriate infrared sauna.
“Compared with our intervention, Waon Therapy uses smaller cabins that heat the skin rapidly and maintain uniform heating of 60°C throughout the cabin. This is due to their compact size, which allows for closer and more uniform exposure to far infrared heating panels. In contrast, the current study used a larger, conventional sauna where participants were not fully exposed to surrounding far infrared heating panels, and the mean temperature during far infrared sauna heating was 45°C.” (1)
Furthermore, the same authors do acknowledge that other studies using Waon therapy (infrared sauna) are able to easily reach a core temperature of 101.5 degrees Fahrenheit after just 15 minutes of infrared sauna use. (3)
Sadly, not all studies can be trusted. What this study does show unequivocally is the importance of actually heating the core temperature up during whatever heat therapy that you choose to use if you want to elicit positive changes for immunity.
It would be a mistake to walk away from this study and think that taking a hot bath for 20 minutes at home is better than taking a sauna when it comes to improving immunity. If you have a hot tub and can set the temperature to 40 degrees celsius or 104 degrees Fahrenheit and stay in for a full 45 minutes, then yes you can absolutely improve your immune response with this form of therapy.
Furthermore, if you use a certified infrared sauna with proper heating panels and size of cabin structure, you will also be able to mimic a moderate fever and therefore improve immune response.
Additionally, it has been proven in thousands of studies that traditional saunas are able to increase core body temperature high enough to elicit an increase in Heat Shock protein production, a precursor for improved T-cell presence. A publication by the National Library of Medicine entitled ‘The effects of a single and a series of Finnish sauna sessions on the immune response and HSP-70 levels in trained and untrained men’ (4) makes it very clear that the use of a traditional sauna can improve immunity, provided that multiple sauna sessions are taken.
“Sauna bathing can be a way to improve the immune response, but only when it is undertaken as a series of treatments.” (4)
While a study can demonstrate some aspects of truth, it is important to pop the hood open and look at what is actually going on before drawing absolute conclusions.
The truth is that if you would like to improve immunity you must use a heat therapy device that propels your internal core temperature to at least 101.5 degrees fahrenheit to induce a moderate artificial fever. If your sauna, or bath are not able to warm you up enough then Heat Shock Protein (HSP) production will not be robust enough to elicit the immune response. Whatever form of heat therapy you choose to use to boost immunity during the coldest months of the year needs to be powerful enough to increase your core temperature so that your body believes that the same alarm bells are being wrung as if there were a natural fever occurring.
Ensure that Your Core Temperature Rises During Heat Therapy to Improve Immunity
Avoid the common cold and flu this winter by improving your immunity with heat therapy, but just remember that you must be able to mimic a moderate fever for the results to transpire. Whether you choose a hot tub, steam room, hot air traditional sauna, or an infrared sauna it is necessary to ensure that your own core temperature is able to reach a high enough temperature to elicit an ‘alarm’ response for your immune system.
Ensure that your body is full of immune boosting cytokines, HSPs, T-cells, and T-cell helpers before you actually get sick by spending time in an environment that induces an artificial fever. Make sure that your focus is on your own internal temperature by using a thermometer that is reliable, instead of just setting the temperature on your device.
Each person is different so choose a heat therapy method that works for you and your body. For an additional boost to your immune system consider using an infrared sauna so that you can optimize your mitochondrial function to ensure that your immune system is fully supported.
Whatever means you choose to support your immune system this winter, just remember that you do need to make sure that you are getting hot and staying hot! Also, maintain excellent hydration at all times and consider using other immune supporting foods, minerals, and vitamins.
If you are unsure if heat therapy is for you, be sure to consult with your health care professional before jumping in!
Sources Cited:
- https://www.ncbi.nlm.nih.gov/books/NBK562334/
- https://journals.physiology.org/doi/full/10.1152/ajpregu.00012.2025
- https://pubmed.ncbi.nlm.nih.gov/19304125/
- https://pubmed.ncbi.nlm.nih.gov/36813265/