Sauna for Cold and Flu: What the Science Actually Says

Sauna for Cold and Flu: What the Science Actually Says

Using a sauna when you have a cold or flu is not straightforward. The short answer: regular sauna use is associated with fewer colds and lower pneumonia risk in some studies, but once symptoms are already present, heat exposure adds physiological stress your body cannot afford. Rest, hydration, and recovery come first. The sauna comes after.

Here is what the research shows, what it does not show, and how to use heat therapy intelligently around illness.

How Sauna Use Affects Your Immune System

The research on sauna and infections is limited but interesting. It comes from a small trial on colds and from long-term Finnish cohort studies. Several mechanisms have been proposed, but none has been proven to explain the findings.

A 2017 study in Respiratory Medicine (Kunutsor et al.) followed 2,210 Finnish men for a median of about 25 years. Men who used a sauna two to three times a week had about 28% lower risk of pneumonia than once-a-week users, and those using it four or more times a week had a lower risk that was borderline in statistical terms. A related analysis linked frequent sauna use with lower risk of respiratory disease in Finnish men (Kunutsor et al., European Journal of Epidemiology, 2017). These are associations, not proof that sauna prevents infection.

The most direct evidence on colds is older and small. In a 1990 study, 25 people who used a sauna regularly caught significantly fewer colds over six months than 25 controls, with the difference most noticeable in the last three months. The duration and severity of colds did not differ, and the authors called for further studies (Ernst et al., Annals of Medicine, 1990).

What Are Heat Shock Proteins and Why Do They Matter?

Heat shock proteins (HSPs) are a family of proteins produced by cells in response to thermal stress. They are one of the proposed mechanisms by which regular heat exposure might influence health.

A 2016 review by Calderwood and colleagues in Frontiers in Immunology describes the complicated roles of HSPs outside cells in immunity, including in antigen presentation, the process by which the immune system identifies pathogens. This is laboratory and mechanistic research. It does not show that sauna use trains the human immune system.

It is a plausible piece of the puzzle, not a proven explanation. For a deeper look at the full evidence base, our evidence-based heat therapy guide covers the research in detail.

Circulation and Immune Cells

When you sit in a traditional Finnish sauna, typically 70–100°C, your core body temperature rises and your cardiovascular system responds quickly. Blood vessels dilate and heart rate increases, similar to light-to-moderate exercise.

Some researchers have suggested that increased circulation during heat exposure may affect how immune cells move around the body, but this has not been shown to reduce infections. The Ernst trial did not identify a mechanism.

What the evidence does suggest is that any benefit comes from regular use over time, not a single session. One session does not protect you from the flu.

If you are building a regular protocol, our guide on how often you should sauna gives frequency recommendations based on your health goals.

Heat Acclimation and Immunity

Repeated heat exposure produces heat acclimation: the body adapts so that later heat exposures cause less physiological strain. Sport scientists use structured heat acclimation to prepare athletes for competing in hot conditions (Pryor et al., Temperature, 2019).

Heat acclimation is well established for heat tolerance. The idea that it also makes you more resilient to infection is a hypothesis, not a research finding.

Because the studies above looked at regular sauna habits, convenient access, such as owning a sauna rather than visiting one occasionally, is what makes regular use realistic.

Should You Use a Sauna When You Have a Cold or Flu?

This is where the nuance matters most. Any benefits described above are preventive and linked to regular use in a healthy state. They do not apply in the same way when you are already sick.

When you have active cold or flu symptoms, your body is already under significant physiological stress. Your core temperature may already be elevated. Your immune system is actively fighting. Your fluid balance is compromised. Adding the thermal load of a sauna session compounds those stressors.

The specific risks during active illness:

• Dehydration accelerates. You are already losing fluids through fever and mucus production. A hot sauna session significantly increases sweat rate, adding to dehydration.
• Cardiovascular load increases. A compromised body managing an infection does not need an additional cardiovascular demand layered on top.
• Symptom severity can worsen. The additional heat stress may intensify fatigue, headache, and body aches rather than relieving them.
• You risk infecting others. If you use a shared sauna, you are exposing other people to your illness in an enclosed, high-humidity environment.

The practical advice is simple: if you have active cold or flu symptoms, skip the sauna. Rest, hydrate, and let your immune system do its work without additional interference.

Once symptoms have fully cleared, not just subsided, you can ease back into your routine. If you have a heart or lung condition, or are unsure, speak to your doctor first. Start with shorter sessions at moderate temperatures and rebuild from there.

Hydration: Non-Negotiable Before, During, and After

Whether you are healthy or recovering, hydration is the foundational variable in any sauna protocol. A typical hot sauna session can cause a significant amount of fluid loss through sweat, more in longer sessions or at higher temperatures.

That fluid loss is manageable when you are healthy and well-hydrated going in. It becomes a genuine risk when you are already depleted from illness. Dehydration reduces blood volume and makes dizziness, headache and fatigue more likely.

Practical hydration protocol for healthy sauna sessions:

Why Sauna Materials Matter

You breathe deeply in a sauna, so the air quality matters. Some home saunas on the Australian market use glued panels, MDF or particle board, and many adhesives are formaldehyde-based. Formaldehyde is classified by IARC (the World Health Organization's cancer agency) as carcinogenic to humans.

The Genesis is built from clear-grade Japanese cedar with no glue, MDF or wood filler. It uses a 9 kW heater, either the Harvia Vega or the HUUM Drop, which holds 60 kg of stones, so the thermal mass holds heat for the full session and the temperature does not collapse every time you pour löyly. Psycle Clean Air active ventilation brings in fresh air and exhausts stale air.

If you are building a regular sauna practice, the cabin you sit in matters. You can read more about what separates real Finnish sauna construction from flatpack alternatives in our complete home sauna buying guide for Australia.

Sauna as Prevention vs Treatment: The Correct Mental Model

The limited evidence for sauna and infections is about prevention through regular use, not treatment. This distinction matters when deciding whether to use a sauna with cold or flu symptoms.

The right question is not "will a sauna cure my cold?" It will not. A better question is whether regular sauna use, alongside sleep, exercise and diet, fits a healthy routine. That is where the evidence, limited as it is, points.

For guidance on session length, our guide on how long to stay in a sauna by goal and experience level gives practical benchmarks.

Does Sauna Temperature Matter for Immune Benefit?

No study has identified a temperature threshold for immune benefit. The Finnish studies asked people about their usual habits in traditional Finnish saunas, which typically run at 70–100°C.

Infrared saunas typically operate at 50–70°C. At those temperatures you still sweat, but the heat load is milder. The Finnish cohort research was done with traditional saunas, and there is no equivalent long-term data for infrared, so the findings should not be assumed to transfer.

If you want the kind of sauna used in the Finnish research, choose one that reaches and holds traditional temperatures. Our comparison of traditional sauna versus infrared covers this in full detail, including where the research diverges between the two formats.

The Genesis heats to traditional Finnish temperatures with a 9 kW heater (Harvia Vega, or HUUM Drop with 60 kg of stones) that holds heat consistently across a full session.

Frequently Asked Questions

Is sauna good for a cold?

Sauna is not a treatment for an active cold. Once you have cold symptoms, the thermal and cardiovascular stress of a sauna session adds load to a body that is already taxed. Any benefit appears to be preventive, linked to regular use while healthy. During illness, rest and hydration are more effective than heat exposure.

Can you use a sauna with flu symptoms?

No. Flu symptoms, particularly fever, body aches, and fatigue, indicate significant physiological stress. Adding sauna heat when your core temperature is already elevated from fever compounds dehydration risk and cardiovascular load. Wait until symptoms have fully cleared, and ideally a couple of days more, before returning to sauna use. If you are unsure, check with your doctor.

Does sauna help prevent colds?

Possibly, for regular users. A small 1990 trial found regular sauna users caught significantly fewer colds over six months (Ernst et al., Annals of Medicine), and a 2017 Finnish cohort study linked sauna use two to three times a week with about 28% lower pneumonia risk in men (Kunutsor et al., Respiratory Medicine). Both need confirming in larger trials, and the mechanism is not known.

How hot does a sauna need to be to boost immune function?

No study has established a temperature threshold for immune benefit. The Finnish studies involved people using traditional Finnish saunas, which typically run at 70–100°C. Lower-temperature formats such as infrared (50–70°C) have not been studied in the same way.

How long after being sick can you use a sauna?

Wait until all active symptoms have fully cleared, and ideally a couple of days more. Return with a shorter, gentler session at a moderate temperature before resuming your full routine. If you had a severe illness, or have a heart or lung condition, speak to your doctor first. For more guidance, see our article on sauna frequency by health goal.

References

Ernst E, Pecho E, Wirz P, Saradeth T. Regular sauna bathing and the incidence of common colds. Annals of Medicine. 1990;22(4):225-227.

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. Respiratory Medicine. 2017;132:161-163. doi:10.1016/j.rmed.2017.10.018

Kunutsor SK, et al. Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. European Journal of Epidemiology. 2017;32(12):1107-1111. doi:10.1007/s10654-017-0311-6

Calderwood SK, Gong J, Murshid A. Extracellular HSPs: the complicated roles of extracellular HSPs in immunity. Frontiers in Immunology. 2016;7:159. doi:10.3389/fimmu.2016.00159

Pryor JL, Johnson EC, Roberts WO, Pryor RR. Application of evidence-based recommendations for heat acclimation: individual and team sport perspectives. Temperature. 2019;6(1):37-49. PMC6422510