The Semmelweis Reflex: when current beliefs trump new knowledge

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Why do we often want to stick with our current beliefs, even when new knowledge seems to contradict them? Why does dogmatic belief habitually trump objective evidence? This effect is called the Semmelweis reflex, which Thomas Szasz described as “the invincible social power of false truths”—a phenomenon so dangerous it has caused many deaths throughout history.

Buckle up for an incredibly sad but illuminating story, where a visionary physician tells the world about a way to save many lives, only to see his own life destroyed.

In 1846, the Vienna General Hospital in Austria was experiencing a troubling problem: its two maternity wards, both housed within the same hospital, had dramatically different maternal mortality rates. The first maternity ward had mortality rates around 10% (sometimes up to 16%), while the second maternity ward had much lower mortality rates, around 4%. Almost all the maternal deaths were due to puerperal fever, a common cause of death in the 19th century.

The two maternity wards admitted on alternate days, but the difference in maternal mortality rates was known outside the hospital, and women begged on their knees to be admitted to the second ward. The reputation of the first maternity ward was so bad, some women preferred to give birth on the street—pretending to have given sudden birth on their way to the hospital, so they could still qualify for childcare benefits.

At the time, a young physician named Ignaz Semmelweis was working at the hospital. He became obsessed with this mystery. Why would maternal rates be so different between maternity wards in the very same hospital? Even more baffling, how come women who gave birth on the street seem to fare better than women admitted in the first ward?

Ignaz Semmelweis - The Semmelweis Reflex

“To me, it appeared logical that patients who experienced street births would become ill at least as frequently as those who delivered in the clinic. (…) What protected those who delivered outside the clinic from these destructive unknown endemic influences?” he wrote.

Breakthrough discovery

The mystery perturbed him so much, he decided to take a break and left for Venice on 2 March 1847. When Ignaz Semmelweis came back to Vienna on 20 March 1847, he learned of the death of his good friend Jakob Kolletschka, who was Professor of Forensic Medicine at the Vienna General Hospital.

This event, while heartbreaking, was the breakthrough Ignaz Semmelweis needed to finally solve the mystery of the two maternity wards: while conducting an autopsy, Jakob Kolletschka pricked his finger with a scalpel, and shortly died from a similar infection to the one afflicting women giving birth at the hospital.

“I was immediately overwhelmed by the sad news that Professor [Jakob] Kolletschka, whom I greatly admired, had died in the interim. The case history went as follows: Kolletschka, Professor of Forensic Medicine, often conducted autopsies for legal purposes in the company of students. During one such exercise, his finger was pricked by a student with the same knife that was being used in the autopsy. (…) Day and night I was haunted by the image of Kolletschka’s disease and was forced to recognize, ever more decisively, that the disease from which Kolletschka died was identical to that from which so many maternity patients died,” Ignaz Semmelweis recorded.

That’s when he found the solution to the seemingly unsolvable problem that had haunted him for so long: there was only one difference between the two wards. The doctors in the first maternity ward were often performing autopsies, which didn’t happen in the second ward. The doctors in the first ward were routinely delivering babies with the same unwashed hands they were conducting autopsies with.

Ignaz Semmelweis proposed that doctors were infecting patients with what he called “cadaverous particles” and immediately insisted that all the medical staff wash their hands in a chlorinated lime solution before treating patients and delivering babies. This simple change resulted in a drop in maternal deaths from puerperal fever to around 1%.

Knee-jerk rejection of the new theory

Despite this scientific breakthrough, the medical community at the time not only showed skepticism, but openly mocked Ignaz Semmelweis for his insistence on the application of antiseptic policies to prevent bacterial infections. Unfamously, Charles Meigs, a leading American obstetrician, noted that “doctors are gentlemen, and gentlemen’s hands are clean.” (it doesn’t help for his legacy that he was firmly against obstetric anesthesia, warning against the morally “doubtful nature of any process that the physicians set up to contravene the operations of those natural and physiological forces that the Divinity has ordained us to enjoy or to suffer”)

“Most medical lecture halls continue to resound with lectures on epidemic childbed fever and with discourses against my theories. (…) In published medical works my teachings are either ignored or attacked. The medical faculty at Würzburg awarded a prize to a monograph written in 1859 in which my teachings were rejected,” wrote Ignaz Semmelweis.

Ignaz Semmelweis was eventually sacked from the Vienna General Hospital. He became severely depressed, and wrote a series of open letters addressed to “all obstetricians” calling them “irresponsible murderers.” He began to drink immoderately, spending progressively more time away from his family, sometimes leaving the company of his wife to spend time with prostitutes instead.

In his biography of Ignaz Semmelweis, K. Codell Carter wrote: “It is impossible to appraise the nature of Semmelweis’s disorder. It might have been Alzheimer’s disease, a type of dementia, which is associated with rapid cognitive decline and mood changes. It might have been third-stage syphilis, a then-common disease of obstetricians who examined thousands of women at gratis institutions, or it might have been emotional exhaustion from overwork and stress.”

On July 30th of 1865, a fellow physician lured him to a recently opened mental asylum under the pretence of visiting the new institution. Ignaz Semmelweis guessed what was happening and tried to leave, but he was severely beaten by several guards, bound in a straitjacket, and placed in solitary confinement. He died after two weeks, aged 47. Very few people attended his funeral. The rules of the Hungarian Association of Physicians specified that a commemorative address be delivered in honour of a member who had died in the preceding year; however there was no address for Ignaz Semmelweis. His death was never mentioned.

More than twenty years later, Louis Pasteur would suggest a theoretical explanation for Semmelweis’ observations: the now widely accepted germ theory of disease.

The Semmelweis Reflex

This knee-jerk tendency to reject new evidence because it contradicts established beliefs is called “The Semmelweis Reflex”—which causes us to easily dismiss new, difficult ideas. It’s a form of confirmation bias where denialism leads us to ignore objective evidence, even if it could bring transformative improvement.

The Semmelweis reflex is still very much present today. For instance, take climate change: in a survey conducted in Australia, the participants who thought climate change was not happening or was caused by natural processes were more likely to select “common sense” as the reason for their belief. Just like 19th century doctors who thought it was common sense for a gentleman’s hands to always be clean.

The transmission mode of COVID-19 is another example. It took months for the CDC to accept the mounting evidence that COVID-19 transmission could be airborne. In fact, it’s only on October 5th, 2020 that they finally updated their website to say that infection can occur from airborne exposure.

There are probably many legitimate scientific discoveries we are currently dismissing; time will tell us that in some cases we were painfully wrong. But we don’t need to wait for a new consensus to form. We can train ourselves to avoid the Semmelweis Reflex by not holding too hard on our beliefs, and keeping an open mind when new evidence presents itself.

How to adopt new knowledge

We tend to stick to what we know—it’s a basic survival mechanism. However, in order to grow, we need to get out of our comfort zone, and learn how to abandon old beliefs to adopt new ones when they are backed by the latest evidence.

  1. Assess your dogmatic beliefs. Dogma is any belief held unquestioningly and with undefended certainty. We all have some dogmatic beliefs, whether when it comes to philosophical positions, political views, and sometimes religion. While you may choose to stick to some of your dogmatic beliefs for personal reasons, it’s crucial to honestly assess their nature as dogma, and to understand how they affect the way you consider new evidence. Dogmatic beliefs may not be obviously negative, which can make them hard to spot. “I believe progress is good”, “I believe property rights should be protected”, “I believe in the benefits of free markets” are all dogmatic beliefs which can seem innocent but will impact your willingness to explore new discoveries.
  2. Make room for genuine curiosity. Every time you have a knee-jerk reaction to a new piece of information, ask yourself why it is the case. What dogmatic belief does the new evidence go against? Which of your current beliefs would you have to abandon in order to embrace the new knowledge? It doesn’t mean you need to blindly accept the new knowledge. Rather, it means you need to make space for honest exploration; to give the new information a chance by trying to really understand it.
  3. Critically accept or reject new findings. Taking into account your existing beliefs and your cognitive biases, apply critical thinking to assess the new evidence. Decide whether you’re convinced or whether you need more information. If you feel like some information is missing, seek to discover whether it exists somewhere, or if more research is needed. A common conclusion in scientific paper is: “These findings suggest that X, however, further research should be conducted.” This is a perfectly valid conclusion after critically considering a new piece of information.

These three steps may not help you completely avoid falling prey to the Semmelweis reflex, but they can lead you to identifying it and managing it better, giving yourself a chance to move past the initial reflex towards a critical assessment of any new evidence you are presented with. If more people were aware of the Semmelweis reflex and actively tried to avoid it, we may accept transformative discoveries much faster.

As for Ignaz Semmelweis, we have finally accepted how transformative his discovery really was.  Nearly two hundred years after his birth, he was immortalised in an Austrian €50 coin, several hospitals and a university have been named in his honour, and his former home was turned into the Semmelweis Medical History Museum. A minor planet is even named after him. Many films and novels were based on his life.

And, of course, his tragic story left us with the concept of the Semmelweis reflex, which we can learn to avoid if we try to not hold too hard on our existing beliefs.