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Key historical events and theories in public health


Now more than ever, public health has become crucial, which looks at promoting health and preventing disease within a society. There have been numerous events and concepts that have helped shape our current health systems today because without them, it is possible that our health systems would not have advanced without previous knowledge to evolve from. This article will focus on certain key events and concepts. 

Humoral Theory (Ancient Greek and Roman times)

To begin, there was the Humoral Theory, which looked at how disease was caused by gaps in fluids/humours which were: blood, yellow bile, black bile and phlegm, which equated to the elements of air, fire, earth and water respectively. The imbalance can come from habits like overeating and too little/much exercise or external factors such as the weather. This theory was thought to have originated from the Hippocratic Corpus, a compilation of 60 medical documents written during the Ancient Greek era by Hippocrates. Although this theory as we know now is flawed, it did provide a foundational understanding of the human body and was utilised in public health for centuries before being subsequently discredited for the Germ Theory established during the mid-19th century.



Miasma Theory (Ancient Greek era to the 19th century)

Another theory replaced by Germ Theory was the Miasma theory, which stated that diseases like the plague and cholera were spread due to toxic vapours from the ground/decomposing matter. This theory along with the Humoral theory was accepted for thousands of years since the Ancient Greek era. With regards to the cholera outbreaks in the Victorian era, John Snow’s theory of polluted water causing cholera was initially not accepted by the scientific community during his death in 1858. Eventually though, his theory became accepted when Joseph Bazalgette worked to fix London’s sewage to prevent more deaths by cholera. This event with the Germ Theory led to Miasma and Humoral theories to be disproved, although they provided foundational understanding of how diseases spread.

The discovery of vaccines (late 18th century)

Aside from theories such as the four humours from above, there were concepts or discoveries that advanced public health measures such as vaccination, which eradicated smallpox and is still used today to prevent the severity of diseases such as COVID-19, influenza and polio. The origins of successful vaccines could be traced back to Edward Jenner who in 1796, retrieved samples from cowpox lesions from a milkmaid because he noticed that contracting cowpox protected against smallpox. With this in mind, he inoculated an 8 year old boy and after this, the boy developed mild symptoms, but then became better.  Without this event, it is likely that the human population would significantly decrease as there is more vulnerability to infectious diseases and public health systems being weaker or less stable. 

Image of a COVID-19 injection.



Germ Theory (19th century)

As for current scientific theories relating to public health, there is the widely accepted Germ Theory by Robert Koch during the 19th century in the 1860s, stating that microorganisms can cause diseases. He established this theory by looking at cow’s blood through a microscope to see that they died from anthrax and observed rod-shaped bacteria with his hypothesis that they caused anthrax. To test this, he infected mice with blood from the cows and the mice also developed anthrax. After these tests, he developed postulates and even though there are limitations to his postulates at the time like not taking into account prions or that certain bacteria do not satisfy the postulates, they are vital to the field of microbiology, in turn making them important to public health.





The establishment of modern epidemiology (19th century)

Another key concept for public health is epidemiology, which is the study of the factors as well as distribution of chronic and infectious diseases within populations. One of epidemiology’s key figures is John Snow, who explored the cholera epidemics in London 1854, where he discovered that contaminated water from specific water pumps was the source of the outbreaks. Moreover, John Snow’s work on cholera earned him the title of the “father of modern epidemiology” along with his work providing a basic understanding of cholera. Therefore, this event among others has paved the way for health systems to become more robust in controlling outbreaks such as influenza and measles.


Looking at the key events above, it is evident that each of them has played an essential role in building the public health systems today through the contributions of the scientists. However, public health, like any other science, is constantly evolving and there are still more future advancements to look forward to that can increase health knowledge.

By Sam Jarada

Related articles: Are pandemics becoming less severe? / Rare zoonotic diseases



  1. Lagay F. The Legacy of Humoral Medicine. AMA Journal of Ethics. 2002 Jul 1;4(7). 

  2. Earle R. Humoralism and the colonial body. Earle R, editor. Cambridge University Press. Cambridge: Cambridge University Press; 2012. 

  3. Halliday S. Death and miasma in Victorian London: an obstinate belief. BMJ. 2001 Dec 22;323(7327):1469–71. 

  4. Riedel S. Edward Jenner and the history of smallpox and vaccination. Proceedings (Baylor University Medical Center). 2005 Jan 18;18(1):21.

  5. National Research Council (US) Committee to Update Science, Medicine, and Animals. A Theory of Germs. National Academies Press (US); 2017. 

  6. Sagar Aryal. Robert Koch and Koch’s Postulates. Microbiology Notes. 2022. 

  7. Tulchinsky TH. John Snow, Cholera, the Broad Street Pump; Waterborne Diseases Then and Now. National Library of Medicine. Elsevier; 2018. p. 77–99. 

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