For as long as Finns have built saunas, they have spoken about the sauna in the language of wellbeing. UNESCO, when it inscribed Finnish sauna culture as Intangible Cultural Heritage in December 2020, used the phrase "to cleanse the body and mind and embrace a sense of inner peace." That language is intentionally cultural rather than clinical, and we have been careful, in these pages, not to dress it up as medicine.
Every so often, though, a piece of research lands that is worth reading on its own terms. A paper published this spring in the journal Temperature is one of those.
What the researchers did
A team led by Professor Jari Laukkanen at the University of Eastern Finland, together with Academy Research Fellow Ilkka Heinonen at the University of Turku, ran a controlled study on 51 middle-aged adults: 27 women and 24 men, with a mean age of 50. Each participant sat in a Finnish sauna at 73 °C for thirty minutes, with a brief cold-shower cool-off midway through the session. The researchers measured immune cells and a wide panel of cytokines (the chemical signals that immune cells use to talk to each other) before, during, and after the session.
The study was published on 31 March 2026 in Temperature, the peer-reviewed journal of body-temperature physiology, and the headline finding is straightforward.
What they found
A single sauna session pushed white blood cells into circulation. Neutrophils and lymphocytes, the most numerous immune cells in the bloodstream, rose during the session and then returned to baseline within about thirty minutes of finishing. A combined group of monocytes, eosinophils, and basophils, which the researchers grouped together as MXD cells, stayed slightly elevated longer.
The chemical-signal side of the picture was quieter than expected. Of the thirty-seven cytokines measured, only two changed significantly after the session, and both went down. A small number more were correlated with how much each person's body temperature had risen, but the white-cell response was not.
In the words of Ilkka Heinonen, quoted in the University of Eastern Finland press release:
"This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from tissues, where they are then redeposited after the session. This kind of periodic release of white blood cells into the bloodstream is beneficial, as once they leave their storage sites, they are better able to patrol the body and respond to pathogens."
In other words, the sauna appears to do something the immune system already does in response to physical exercise: send circulating cells out on patrol, then return them to storage. It is a mobilisation effect, not a chemical alarm.
What the researchers did not claim
This is where the iHKA house style matters. The study looked at a single sauna session and its immediate effects, not at long-term health. The researchers say so explicitly in the press release accompanying the paper: "no definite conclusions can be drawn about the development of longer-term health effects" from this study alone.
There is a wider literature suggesting that regular Finnish sauna bathing is associated with lower risks of several conditions, much of it from Professor Laukkanen's own earlier work. That is a separate question, and one we will not try to settle in a single journal post. The new finding is narrower and more specific: thirty minutes of heat does measurable things to the immune cells in your blood, in real time.
Why it fits the Finnish tradition
What we find quietly satisfying about this study is how closely it tracks the way Finns have always used the sauna. The protocol the researchers chose, thirty minutes at 73 °C with a cool-off in the middle, is not a clinical contrivance. It is, more or less, an ordinary Saturday evening in Finland. The cyclical pattern of heat, cool, heat is the practice UNESCO recognised, and it is the pattern that produced the response the researchers measured.
We will not turn the sauna into a piece of medical equipment. It is not one. But when a careful, peer-reviewed study uses the genuine Finnish sauna, at a genuine Finnish temperature, with a genuine Finnish cooling break, and finds that the body responds in coherent and measurable ways, it is worth noting. The tradition has its own quiet evidence behind it.
A note on sources
This article is based on two reports of the study by News-Medical (9 April and 17 April 2026) and on the original journal record. The full paper is published in Temperature and can be reached through the DOI link below.
Sources
- Heinonen, I. H. A., Koivula, T., Hollmén, M., Immonen, J., Kunutsor, S. K., Jalkanen, S., & Laukkanen, J. A. (2026). Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses. Temperature. DOI: 10.1080/23328940.2026.2645467
- University of Eastern Finland press release, reported in News-Medical, "Sauna bathing boosts white blood cells for better immune defense," 9 April 2026: news-medical.net
- Thomas, L., "A single sauna session boosts immune cells within minutes," News-Medical, 17 April 2026: news-medical.net
- UNESCO inscription of Finnish sauna culture, December 2020.
Frequently asked questions
What did the new Finnish sauna and immune system study find?
A single 30-minute Finnish sauna session at 73 °C pushed white blood cells, including neutrophils and lymphocytes, into circulation during the session. The cells returned to baseline within about thirty minutes after finishing. The cytokine response was unexpectedly quiet: only two of thirty-seven measured cytokines changed significantly, and both went down.
How was the study designed?
A team led by Professor Jari Laukkanen at the University of Eastern Finland and Academy Research Fellow Ilkka Heinonen at the University of Turku enrolled 51 middle-aged adults (27 women, 24 men, mean age 50). Each participant sat in a Finnish sauna at 73 °C for thirty minutes, with a brief cold-shower cool-off midway through. Blood samples were taken before, during, and after the session.
Does this prove that sauna bathing strengthens immunity long-term?
No. The researchers were explicit on this point: the study looked at a single sauna session and its immediate effects, not long-term health outcomes. The press release accompanying the paper states that no definite conclusions can be drawn about longer-term health effects from this study alone.
Where was the research published?
The paper was published on 31 March 2026 in Temperature, the peer-reviewed journal of body-temperature physiology, under the title "Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses."
Why does this matter for Finnish sauna culture?
The study used a genuinely Finnish protocol: thirty minutes at 73 °C with a cool-off in the middle. That is not a clinical contrivance, but more or less an ordinary Saturday evening in Finland. UNESCO inscribed Finnish sauna culture as Intangible Cultural Heritage in 2020. The findings show that the body responds in coherent, measurable ways to exactly the cyclical heat-cool-heat practice Finns have used for centuries.
