The Nazi Hypothermia Experiments Whose Results Are Still Used Today

Among the most horrific facets of the Holocaust were the medical experiments performed by Nazi doctors upon concentration camp inmates. This sadistic practice was epitomized by the work of Josef Mengele, the ‘Angel of Death,’ who between 1943 and 1945 performed hundreds of cruel human experiments at the Auschwitz-Birkenau extermination camp – including on over 1000 pairs of twins, of whom only 200 survived the war. But Mengele was far from alone; dozens of doctors and researchers took advantage of a seemingly endless supply of expendable human bodies to advance medical science in the name of Third Reich. In Auschwitz’s Cell Block 10, gynaecologist Carl Clauberg experimented on Jewish and Romani women to develop efficient methods for sterilizing those the Nazi regime saw as ‘undesirable’, while at the Natzweiler-Struthof camp anatomist August Hirt murdered inmates for display in an anthropological ‘Jewish Skeleton Collection.’ After the war, nearly all these sadistic experiments were declared unscientific and their results worthless – with one major exception. A series of experiments on hypothermia, conducted at the Dachau Concentration Camp between 1942 and 1943, produced data so medically valuable that they are still cited by researchers to this day. The continued use of this data has unleashed a storm of controversy, at the heart of which lies a pivotal ethical question: is it ever right to use Nazi research, even if it has the potential to save lives?

The Dachau hypothermia experiments were the brainchild of SS doctor Sigmund Rascher. Born on February 12, 1909 to physician Hanns-August Rascher, in 1933 Sigmund followed in his father’s footsteps and began studying medicine in Munich, receiving his doctorate in 1936. During this period he also became a member of the Nazi Party and joined the SA, Hitler’s infamous Brownshirts. From the beginning Rascher displayed great ambition and ruthlessness, and in 1939 in order to advance his career he denounced his father as a traitor and transferred into the SS, which had replaced the SA as Hitler’s personal protection force. Then, following the invasion of Poland in September of that year, Rascher was conscripted into the Luftwaffe, the German Air Force.

Rascher began his research career in 1941, studying the potential anti-cancer effects of various plant extracts. While Kurt Blome, his superior at the Reich Research Council, favoured testing these extracts on rats and mice, Rascher insisted on using human test subjects, and asked Reichsfuhrer Heinrich Himmler, head of the SS, to place a supply of concentration camp inmates at his disposal. When Himmler refused, Rascher’s wife Karoline Diehl, a former cabaret singer, intervened on his behalf. The exact nature of Himmler and Diehl’s relationship is unknown, with some historians speculating that the two had once been lovers. Whatever their connection, Diehl succeeded in convincing the Reichsfuhrer to establish a Human Cancer Testing Station at Dachau concentration camp outside Munich. Having such a powerful ally at the very top of the Nazi establishment would prove invaluable to Rascher’s career, as the official record of the Nuremberg War Crimes Trial would state:

Because of Rascher’s servile and ingratiating approach to Himmler, his connections were so strong that practically every superior trembled in fear of the intriguing Rascher who consequently held a position of enormous power.”

Shortly after arriving at Dachau, Rascher transitioned to research on high-altitude physiology on behalf of the Luftwaffe. These experiments involved placing subjects in an altitude chamber and subjecting them to extreme changes in pressure to simulate bailing out of an aircraft at high altitude. They would then be dissected as quickly as possible so the effects could be studied before their hearts stopped beating. In his correspondence Rascher was unequivocal about the lethal nature of these experiments, leading Himmler to suggest that any test subjects who survived the ordeal be spared the death penalty and given life sentences instead. In the end, of the 200 prisoners tested, 80 died outright – mostly of cerebral embolism – while the remainder were summarily executed.

Other experiments conducted by Rascher during this period involved Polygal, an experimental anti-clotting medication called based on apple pectin. To study its effectiveness on combat wounds, Rascher amputated inmates’ limbs without anaesthesia or had them shot in the neck and chest. He also collaborated with Dr. Hans Eppinger on experiments to determine whether pilots shot down at sea could survive by drinking seawater. For up to 12 days, 90 Romani prisoners were given nothing to drink but seawater, sometimes treated with a tomato-based mixture called Berkatit to mask its taste.The test subjects became so dehydrated that they took to licking freshly-mopped floors to get a single drop of fresh water.

In August 1942 Rascher began the experiments for which he would be best remembered. The hypothermia study was intended to save the lives of Luftwaffe pilots shot down over the North Sea. While immersion in these frigid waters could lead to death within an hour, even pilots who were rescued in time often experienced a mysterious “afterdrop” in body temperature and died soon after. Rascher sought to discover the cause of this phenomenon and determine the best way of rewarming rescued pilots.

Together with assistants Drs. Holzlöhner and Finke, Rascher immersed test subjects – mostly Soviet prisoners of war – in baths of ice water cooled to between 12 and 2 degrees Celsius. Some were immersed naked, others dressed in Luftwaffe flight gear, their vital signs being monitored via EKG and rectal thermometer. Others were left naked in the winter cold for up to 14 hours.

Witnesses later recalled the horrifying effects of these experiments, describing how subjects screamed as their extremities froze solid, then slipped into unconsciousness as their body temperature plummeted. Subjects who did not immediately die were removed from the tank and subjected to various rewarming methods, including warm baths, massages, and banks of heat lamps. Some were even immersed in boiling water – with predictably horrifying results. At the suggestion of Heinrich Himmler, who believed strongly in German “folk science”, Rascher travelled to the Baltic coast to learn how the local people dealt with cases of hypothermia. After speaking to a fisherwoman who had revived her husband using her own body heat, Rascher forced female inmates to lie next to recently-frozen test subjects in order to rewarm them.

Between August 1942 and May 1943, Rascher conducted nearly 400 experiments on 300 inmates, only two of which survived the war. While his data confirmed the existence of the post-immersion “afterdrop,” he was unable to pinpoint its cause, though he did determine that a temperature of 5 degrees could be tolerated by a clothed man for up to an hour and 15 degrees for up to 5 hours without ill effect; that death from hypothermia occurred at an average body temperature of 27 degrees Celsius; and that the best method for rewarming hypothermia victims was immediate immersion in warm water. Thanks to this and other research conducted at Dachau, Rascher was held in high regard among top Nazi officials – including Hitler himself. His reputation among his fellow scientists, however, was considerably less stellar, with Professor Karl Gebhard, Heinrich Himmler’s personal physician, stating of Rascher’s final report on the hypothermia experiments:

[It is] unscientific; if a student of the second term dared submit a treatise of the kind I would throw him out.”

Rascher’s strong connections with top officials allowed him to brush off such criticisms, but not even Himmler could save him from the spectacular fall from grace he was about to suffer.

In early 1944, Rascher revealed to Himmler that his wife had given birth to three healthy children in quick succession despite being 48 years old. Himmler, obsessed with finding ways of increasing the national birthrate, eagerly agreed to fund Rascher’s fertility studies. But in April of that year Karolein Rascher was caught trying to kidnap a baby, and it soon became clear that all three of her supposed ‘miracle’ children had actually been obtained in this manner. The Raschers were arrested on charges of fraud and sent to Dachau – becoming, in an ironic twist of fate, prisoners in the same camp over which they had once presided. On April 26, 1945, a mere three days before American troops liberated the Dachau, Sigmund Rascher was executed via a pistol shot to the head, his executioner, Theodore Bongartz, supposedly exclaiming:

You pig, now you’ve got the punishment you deserve.”

By the time Dachau was liberated, much of the documentation regarding the hypothermia experiments had been destroyed by the retreating Germans. However, Allied investigators uncovered extensive correspondence between Rascher and Himmler along with a number of interim research reports, which formed the basis of a comprehensive 228-page report prepared by Dr. Leo Alexander, chief medical consultant for the Nuremberg War Crimes Trials.

While much of the research conducted by Nazi doctors on concentration camp inmates was dismissed as little better than quackery, Sigmund Rascher’s hypothermia studies lived on. By 1984 more than 45 scientists had directly cited the Dachau experiments in their work, including Robert Pozos, director of the Hypothermia Laboratory at the University of Minnesota Medical School. According to Pozos, current methods for treating hypothermia victims are based on trial-and-error performed in hospital emergency rooms and vary wildly in their application and effectiveness. And while Pozos has conducted some laboratory experiments on hypothermia using volunteer test subjects, for ethical reasons the subjects’ body temperatures are never allowed to drop below 36 degrees Celsius. Rascher’s results, being the only empirical data in existence on what happens to the human body at low temperatures, may thus hold the key to gaining a more rigorous understanding of hypothermia and developing effective methods for treating it. Yet despite these noble intentions, Pozos’ plan to republish Rascher’s data in a paper for the New England Journal of Medicine was flatly vetoed by the journal’s editor.

Another proponent of using the Dachau data is John Hayward, a hypothermia expert at the University of Victoria, British Columbia. Combining Rascher’s body temperature cooling curves with those obtained from consenting volunteers at higher temperatures, Hayward developed a mathematical model to predict how long a person can survive when immersed in cold water – information vital to search-and-rescue teams. Regarding the origins of the data, Hayward stated:

I don’t want to have to use the Nazi data, but there is no other and will be no other in an ethical world. I’ve rationalized a bit. But not to use it would be equally bad. I’m trying to make something constructive out of it. I use it with my guard up, but it’s useful.”

Like Pozos, Hayward has run afoul of those who believe Nazi data cannot be ethically used regardless of its supposed usefulness, such as Arnold Relman, the editor-in-chief of the New England Journal of Medicine who vetoed Robert Pozos’ article:

[The experiments] are such a gross violation of human standards that they are not to be trusted at all.”

This sentiment is further echoed by Dom Wilkinson stated, a medical ethicist at Oxford University:

The basic intuition is that if information had been obtained unethically, but we use that information, then we then become complicit in that past. There’s something very particular about knowledge, that it’s irreversible. You can’t unknow something. One concern of using the data is that it expresses the attitude that this research was okay, and encourages future researchers – ‘history will judge me positively’. We want to not do that. We don’t want to promote unethical research.”

While this debate has wide-ranging ethical implications for the whole of medical science, recent reexaminations of Rascher’s original data reveal that it might not actually be as useful as originally assumed. In his 1990 paper Nazi Science – The Dachau Hypothermia Experiments, Dr. Robert Berger identifies hundreds of glaring mistakes, inconsistencies, and oversights in Rascher’s reports which bring their much-touted scientific rigour into serious doubt. For example, rarely does Rascher record the age, weight, or other vital statistics of his test subjects, and while the report concludes that the best rewarming method is immersion in warm water, no data is provided to back up this assertion. Furthermore, in his reports to Himmler, Rascher states that all subjects died after 50-100 minutes, but the data and reports from observers reveal that most took at least 80 minutes to die, with many clothed subjects surviving for up to 7 hours. Statements of the average lethal temperature are similarly all over the place, with the report stating 28 degrees but the data recording temperatures as low as 25.2.

But especially damning are the many instances where Rascher records observations now known to be medically impossible. For example, in one experiment Rascher claims that the subject continued to breathe for a full 20 minutes after their heart stopped. In another, Rascher concludes that death was due to cold-induced injury to the heart, even though we now know that low temperatures actually protect the heart. In fact, medically-induced hypothermia is commonly used to reduce damage to the heart and brain in cases of cardiac arrest. Finally, Rascher describes the swelling and bleeding of the brain, while modern clinical observations reveal that hypothermia actually shrinks the brain.

According to Berger, these inconsistencies point to much of Rascher’s data being altered or outright fabricated, likely in an attempt to support his and Himmler’s pet theories. For example, Himmler believed that the back of the neck was a particularly important region for heat loss, and that hypothermia could be significantly delayed if this area was kept above the surface of the water. Rascher’s experimental data confirm this hypothesis, even though in reality far more heat is lost through the scalp than the back of the neck. In light of these and other fabrications, Berger concludes that none of Rascher’s results can be trusted.

Why, then, did so many researchers continue to cite the Dachau experiments as accurate? Berger traces this misconception back to Dr. Leo Alexander, who, after completing his concluded stated that Rascher’s reports contained medically valuable data. While Alexander later retracted this statement, Berger speculates that many researchers continued to cite his initial flawed analysis rather than actually reading Rascher’s original data and reports. Thus, far from being the sole example of “good” Nazi science, it appears that the Dachau hypothermia experiments were in fact no more scientific than injecting dye into people’s eyes or sewing twins together. They were part and parcel of a monstrous program of pseudoscience and inhuman torture, the likes of which we can only hope we will never see again.

Expand for References

Oord, Christian, From Himmler’s Darling to Dachau Inmate: The Fraudulent Nazi Doctor, War History Online, March 18, 2019,

Mackowski, Maura, Testing the Limits: Aviation Medicine and the Origins of Manned Space Flight, Texas A&M Press, 2006,

Berger, Robert, Nazi Science – The Dachau Hypothermia Experiments, The New England Journal of Medicine, May 17, 1990,

Swain, Frank, Is it Right to use Nazi research if it can Save Lives? BBC, July 23, 2019,

Cohen, Baruch, Nazi Experimentation: The Ethics of Using Medical Data From Nazi Experiments, Jewish Virtual Library,

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