Heat & Sauna - The basics
Heat-shock proteins and the hormetic response
Last updated 29 September 2026. How we write this .
Heat-shock proteins help other proteins keep their shape under stress. Sauna-style heat can raise some of them in human blood, but no study shows that doing so improves health or extends life.
Start here Heat-shock proteins help other proteins keep their shape under stress. Sauna-style heat can raise some of them in human blood, but no study shows that doing so improves health or extends life.
By the end, you will understand What are heat-shock proteins? Why are heat-shock proteins linked to ageing? Does a sauna raise heat-shock proteins in people? Key words used in this lesson Meta-analysis A statistical method for combining the results of multiple studies into a single estimate. More reliable than any one study, but bounded by the quality of what went into it. Full plain-English glossary
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Heat-shock proteins are proteins your cells make to protect other proteins when heat or other stresses threaten to damage them. Most work as chaperones, holding vulnerable proteins in shape or helping them refold. In people, a sauna session can raise some heat-shock proteins in the blood, but the human studies are small and mixed, and none shows that raising them improves health or extends life.
What are heat-shock proteins?
They were found by accident. In the early 1960s the Italian geneticist Ferruccio Ritossa was studying fruit fly salivary glands in Pavia and Naples. Someone in the lab shifted the temperature of his incubator, and he saw a burst of new gene activity, visible as fresh swellings called puffs on the flies' chromosomes. He published the finding in 1962. It became known as the heat shock response, and the proteins it produces as heat-shock proteins, or HSPs.
The name stuck, but heat is only one trigger. HSPs respond to many kinds of stress that can damage proteins. They come in families named roughly by their size, such as HSP70 and HSP90. HSP72, the form most studied in sauna research, is a member of the HSP70 family that cells make in larger amounts under stress.
To see why they matter, think about what a protein is. It is a long chain of building blocks that must fold into a precise three-dimensional shape to work. As Ulrich Hartl and colleagues at the Max Planck Institute of Biochemistry explained in a 2011 Nature review, new proteins are at real risk of folding wrongly and clumping together, and these clumps can be toxic. Chaperones prevent the clumping and help proteins fold properly. Because proteins keep moving and changing shape, this surveillance has to be constant. The whole upkeep system is called proteostasis, short for protein balance.
Why are heat-shock proteins linked to ageing?
Hartl's review notes that the capacity of this system appears to decline with age, which may allow protein-clumping diseases such as Alzheimer's and Parkinson's to appear. That idea has driven a lot of interest in whether boosting heat-shock proteins could slow ageing.
The strongest support comes from worms. In 2003 Ao-Lin Hsu, Coleen Murphy and Cynthia Kenyon at the University of California, San Francisco studied HSF-1, the master switch that turns on the heat shock response in the roundworm Caenorhabditis elegans. Reducing HSF-1 made the worms' tissues age faster and shortened their lives. Adding extra HSF-1 lengthened them. Small heat-shock proteins also delayed the clumping of a disease-linked protein. These are striking results, but they come from a tiny worm with a short life, and lifespan genes in worms do not map neatly onto people.
Does a sauna raise heat-shock proteins in people?
Sometimes, depending on what is measured. HSPs do their main work inside cells. Researchers often measure the amount floating in the blood instead, called extracellular HSP, because a blood sample is far easier to take than a muscle sample. Blood levels are an indirect signal, and the two do not always move together.
In a 2012 University of Iowa trial led by Masaki Iguchi, 25 healthy young adults sat for 30 minutes in a heat chamber at 73°C on one day and at 26°C on another. In the heat, rectal temperature rose by 0.8°C, heart rate climbed to an average of about 131 beats a minute and systolic blood pressure fell by 16 mmHg. In the 13 people who gave blood samples, HSP72 in the blood rose by an average of 48.7%, though the spread between individuals was wide.
A 2018 Loughborough University study by Hoekstra and colleagues looked inside cells. Ten inactive men with overweight sat in water at 39°C for an hour. HSP72 inside their monocytes, a type of white blood cell, did not change. After 10 hot baths over two weeks, their fasting blood sugar and insulin had fallen compared with a control group, yet resting HSP72 inside cells was still unchanged and HSP72 in the blood had dropped by 17%. Whatever helped their blood sugar, rising HSP72 was not an obvious explanation.
Pooling the wider evidence, the 2016 meta-analysis of 96 heat adaptation studies by Christopher Tyler and colleagues at the University of Roehampton found that repeated heat exposure had only a trivial effect on blood HSP levels, even while it clearly improved heat tolerance.
Are low heat-shock proteins linked to disease?
There are hints. In a 2002 study in the journal Diabetes, Istvan Kurucz and colleagues took muscle samples from people with type 2 diabetes and healthy controls. In one group of six patients and six controls, the patients had about a tenth as much HSP72 genetic message in their muscle. In a second group of 12 twin pairs where only one twin had diabetes, both twins had much lower levels than unrelated healthy people, and lower levels tracked with poorer insulin sensitivity. The authors posed this as a question, not an answer: low HSP72 could help cause insulin resistance, or result from it.
What is still unknown?
The popular story runs from heat to more heat-shock proteins to better health to a longer life. Each link has been studied separately, in different species and with different measures, but no human study has followed the whole chain. People often point to the Finnish Kuopio cohort, where Tanjaniina Laukkanen and colleagues reported in 2015 that, among 2,315 middle-aged men followed for about 20 years, those who used a sauna 4 to 7 times a week had fewer cardiac and overall deaths than once-a-week users. That was an observational study of sauna habits. It did not measure heat-shock proteins, and it cannot show that sauna, let alone HSPs, caused the difference.
Heat also puts real strain on the circulation, as the 16 mmHg drop in blood pressure in the Iowa study shows. If you have a heart condition or low blood pressure, ask your GP before using a sauna. Confusion, hot skin that has stopped sweating, a fit or collapse in the heat are signs of heatstroke and need a 999 call.
This lesson explains the biology of heat-shock proteins for general education. It is not medical advice and does not recommend any heat routine or product.
Related in this classroom Related in other classrooms The studies behind this page Ferruccio Ritossa's scientific legacy 50 years after his discovery of the heat shock response: a new view of biology, a new society, and a new journal - Cell Stress and Chaperones, 2012Molecular chaperones in protein folding and proteostasis - Nature, 2011Regulation of aging and age-related disease by DAF-16 and heat-shock factor - Science, 2003Heat stress and cardiovascular, hormonal, and heat shock proteins in humans - Journal of Athletic Training, 2012Acute and chronic effects of hot water immersion on inflammation and metabolism in sedentary, overweight adults - Journal of Applied Physiology, 2018The effects of heat adaptation on physiology, perception and exercise performance in the heat: a meta-analysis - Sports Medicine, 2016Decreased expression of heat shock protein 72 in skeletal muscle of patients with type 2 diabetes correlates with insulin resistance - Diabetes, 2002Association between sauna bathing and fatal cardiovascular and all-cause mortality events - JAMA Internal Medicine, 2015Further reading
Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.