What Really Happens to Your Body in a Sauna
You feel the heat. Your heart rate rises. You start to sweat. But something much more interesting is happening at the cellular level. When you sit in a sauna, your body is exposed to a temporary, controlled form of heat stress. As your body temperature rises, your cells activate a protective response known as the heat shock response. One of the most important parts of this response is the production of heat shock proteins, or HSPs. Think of Heat Shock Proteins as Your Cells’ Repair Crew Proteins need to maintain a very specific three-dimensional shape to function properly. Heat can cause some proteins to partially unfold or become unstable. In response, your body increases heat shock proteins — particularly proteins such as HSP70. These proteins act as molecular chaperones. They help other proteins maintain or recover their correct structure, prevent damaged proteins from clumping together, and assist the cell in removing proteins that can no longer be repaired. HSP70 helps heat-stressed proteins recover their shapeFolded proteinCorrect 3D shape,fully functionalHeat stressShape partly unfolds,protein becomes unstableHSP70HSP70 steps inChaperone helps it refoldand prevents clumpingRefoldHelp proteins keep orrecover their shapePrevent clumpingKeep damaged proteinsfrom aggregatingClear the unrepairableHelp the cell removeproteins beyond repair Molecular chaperones: from heat stress to refolding In simple terms: Sauna heat sets off a chain that ends in cellular protectionSaunacontrolled heatHeat stressbody temp risesHeat shockresponsecells sense stressHeat shockproteinse.g. HSP70Protectionand repairproteins kept working The heat shock pathway This is one reason researchers are so interested in sauna and other forms of controlled heat exposure. What Does This Have to Do With Your Immune System? Heat shock proteins aren’t only involved in protein repair. They also interact with the immune system and participate in processes such as immune signaling and antigen presentation — mechanisms that help immune cells recognize what is happening inside the body. Acute heat exposure can also temporarily change the circulation and activity of several immune cells, including lymphocytes, neutrophils, and natural killer (NK) cells. Heat reaches the immune system along two routesAcute heatexposureVia heat shock proteinsImmune signalingAntigen presentationVia circulating immune cells (temporary shifts)LymphocytesNeutrophilsNK cellsNK cells: innate first-line defense against virus-infected and abnormal cells Heat and immunity: two routes NK cells are particularly interesting because they are part of our innate immune system — the body’s rapid first-line defense. They help identify and destroy certain virus-infected and abnormal cells. A note on nuance. This doesn’t mean that one sauna session will suddenly “boost” your immune system or prevent you from getting sick. The science is more nuanced. What we can say is that heat exposure creates a biological stress signal that activates cellular protective pathways and influences several components of immune function. Heat Is the Stress. Adaptation Is the Point. This is an example of hormesis: a small, temporary stressor activates the body’s adaptive defense mechanisms. Exercise works through some of the same principle. Hormesis: a moderate dose of stress drives adaptationAdaptive zonea manageable dose drives adaptationToo muchoverloadBenefitNeutralHarmHeat dose Hormesis: a schematic dose–response curve During a sauna session, the goal isn’t to eliminate heat stress completely. The heat itself is what creates the physiological stimulus. The goal is to experience that heat comfortably and intentionally. And that’s where a sauna hat comes in. Why Wear a Sauna Hat? Your head is directly exposed to the hottest air in the sauna. A wool sauna hat creates an insulating layer around the head and hair, helping reduce the intensity of direct heat exposure. For many people, that makes high-temperature sessions feel significantly more comfortable. It doesn’t stop your body from experiencing the heat. It simply helps you manage it. At LöylyCraft, we think of the sauna hat as part of a smarter sauna ritual: let the body experience the heat while protecting one of the areas where that heat can become uncomfortable first. Heat is the stimulus. Adaptation is the response. Comfort helps you stay with the ritual. That is the intelligent way to sauna. Further Reading Kregel KC. Heat shock proteins: modifying factors in physiological stress responses and acquired thermotolerance. Journal of Applied Physiology, 2002. Pilch W et al. Effect of a single Finnish sauna session on white blood cell profile and cortisol levels in athletes and non-athletes. Journal of Human Kinetics, 2013. 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. International Journal of Hyperthermia, 2023. Laukkanen JA et al. Cardiovascular and other health benefits of sauna bathing: a review of the evidence. Mayo Clinic Proceedings, 2018. This article is for general education and is not medical advice. If you are pregnant or have a heart condition or other health concern, talk to your doctor before using a sauna.
