If you have ever stepped out of a sauna feeling as though your whole body has come alive, new research suggests that the sensation is not only in your head.
A 2026 Finnish study took blood from 51 adults before a sauna, immediately afterwards and again 30 minutes later. After one 30-minute session, every type of circulating white blood cell the researchers measured had increased.
The result was temporary, but it was clear. Heat had changed where the body’s immune cells were and how actively they were moving through the bloodstream.
That gives us a much more useful explanation than the loose phrase “boost your immune system”. A sauna does not fill you with brand-new immunity. It appears to call more of your existing immune patrol into circulation.
The study in plain English
The peer-reviewed study, published in Temperature, involved 27 women and 24 men with an average age of 50.
Each person completed 30 minutes in a traditional Finnish sauna. The average temperature was 73°C with low humidity. After the first 15 minutes, participants took a two-minute shower before returning to the heat. They were given water throughout the session and recovery period.
The researchers measured body temperature, plasma volume, white blood cells and 37 different cytokines. Cytokines are signalling proteins that help immune cells communicate.
By the end of the session:
- Average measured body temperature had risen from 36.4°C to 38.4°C.
- Total white blood cell count had increased.
- Neutrophils, lymphocytes and a mixed group containing monocytes, eosinophils and basophils had all increased in the bloodstream.
- Neutrophils and lymphocytes returned to their starting levels within 30 minutes.
- The mixed cell group remained elevated at the final measurement.
Importantly, the researchers adjusted the blood results for changes in plasma volume. That means the rise in immune cells was not simply an illusion caused by sweating and having less fluid in the blood.
The cells had genuinely moved.
Your immune patrol has left the station
White blood cells are not normally circling through your bloodstream all at once. Many are held in tissues and other storage sites, ready to be deployed.
Think of them like a citywide emergency service. Some teams are on the road while others are waiting at stations around the body. A controlled physical stress, such as exercise or sauna heat, can temporarily send more of those teams into circulation.
This is known as immune surveillance. Once mobile, immune cells are better placed to travel through the body, encounter potential threats and respond where they are needed.
Neutrophils are rapid first responders. Lymphocytes include cells that recognise specific threats, coordinate immune activity and produce antibodies. Seeing both groups rise immediately after the sauna suggests that heat can create a broad, rapid response rather than shifting only one narrow marker.
The fact that the counts returned towards normal soon afterwards is not a failure. It is what a responsive system should do: mobilise when challenged, then settle.
More movement, not necessarily more inflammation
The cytokine results make the study particularly interesting.
Researchers tested 37 cytokines, but only two changed significantly across the group. At the same time, changes in several cytokines were associated with how much an individual’s body temperature rose.
In other words, heat appeared to influence immune signalling, but it did not simply cause every inflammatory marker to surge.
That matters because a healthy response is not about keeping the immune system permanently switched on. Chronic immune activation is not desirable. The more useful goal is flexibility: the ability to respond appropriately to a challenge and then return to balance.
Sauna is a short, deliberate dose of heat stress. Your heart rate rises, blood vessels widen, sweating increases and temperature regulation has to work. That temporary challenge is part of what makes the experience physiologically meaningful.
Does this mean sauna stops you getting ill?
This study was designed to show what happened in the blood after one sauna session. It did not test whether participants caught fewer colds, recovered from infections faster or developed stronger long-term immunity.
There are encouraging clues from other research.
A small six-month controlled trial found roughly half as many common-cold episodes in the sauna group during the final three months, although the trial included only 50 people and needs modern replication.
A long-term Finnish cohort study also found that men who used a sauna more frequently had a lower rate of hospital-diagnosed pneumonia over more than 25 years. That was an association, not proof that sauna alone caused the difference.
The new 2026 study helps connect those observations to a plausible short-term mechanism. It shows that sauna heat can mobilise immune cells. It does not prove that one session prevents an infection, and it certainly does not replace sleep, movement, good nutrition, vaccination or medical care.
The confident conclusion is still an exciting one: sauna is not passive. Even while you sit still, your body is responding.
Why this matters as winter arrives
The useful lesson is not to wait until you feel ill and then try to sweat it out. If you have a fever or an active infection, adding more heat can increase strain and dehydration. Rest and follow appropriate medical advice instead.
The better approach is to make recovery part of ordinary life while you are well.
Regular sauna gives you a repeatable ritual that combines controlled heat exposure with time away from screens, physical stillness and a deliberate transition out of the day’s noise. The immune-cell response is one more reason that ritual may matter.
At R1SE, we have now guided more than 10,000 people through sauna and cold experiences, from nervous first-timers to professional athletes. The people who gain the most are rarely those chasing the longest or hottest session. They are the ones who use an appropriate dose, return consistently and pay attention to how their body responds.
A practical way to begin
The research protocol used 30 minutes of Finnish sauna with a short shower halfway through. That does not mean everyone should copy it on their first visit.
If you are new to sauna, begin with 8 to 12 minutes at a manageable temperature. Step out while you still feel composed, cool down, drink water and only return for another round if you feel well.
With experience, you can build towards longer sessions. Hydrate before and afterwards. Never use discomfort as a scoreboard, and leave the heat immediately if you feel dizzy, nauseous, faint or unwell.
The study used a brief shower, not an ice bath, so it cannot tell us whether a full Fire & Ice cycle would produce exactly the same immune response. Contrast therapy brings its own powerful experience, but it should not be presented as identical to the research protocol.
You can explore the practical options in our sauna guide, read the wider evidence in The Science of Sauna, or discover Fire & Ice at R1SE Sheffield.
The bigger picture
One sauna session will not make you invincible. It can, however, create a rapid and measurable change in your physiology.
Thirty minutes of controlled heat mobilised the body’s immune patrol, altered aspects of immune signalling and then allowed much of the response to settle within half an hour.
That is the point of good recovery practice. It is not about doing nothing. It is about giving the body the right challenge, then giving it the conditions to adapt.
Your immune system is always moving, communicating and learning. Sometimes, sitting in the heat is enough to remind you just how active your body can be.
Discover sauna and Fire & Ice at R1SE Sheffield
Sources
- Heinonen IHA, Koivula T, Hollmén M, et al. Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses. Temperature. 2026;13(2):186-199.
- University of Eastern Finland. Sauna bathing may boost immune responses. 2 April 2026.
- 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. Respiratory Medicine. 2017;132:161-163.
- Kunutsor SK, Laukkanen T, Laukkanen JA. Longitudinal associations of sauna bathing with inflammation and oxidative stress. Annals of Medicine. 2018;50(5):437-442.