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What links: cigarettes, psoriasis and John Snow?


My name is Alex Trafford and I am a second year Epidemiology PhD student in the Division of Pharmacy and Optometry. I have quite a diverse academic background for somebody in my field, being unsure of which subjects I enjoyed most at school and splitting my A-levels between the sciences and humanities. I eventually decided to pursue an undergraduate degree in geography, with two years at Lancaster University and one year abroad at the University of North Carolina. In my final undergraduate year I took part in a module looking at health geographies - during this time I came across the field of epidemiology, which combined aspects of science and humanities, and decided that this was the direction I wanted to go in. In order to learn more about the field, I completed a master’s degree in Demography and Health at the London School of Hygiene and Tropical Medicine in 2017.

In late 2017, I received funding from the Global Psoriasis Atlas and started my PhD in Epidemiology at Manchester. My project here involves using huge datasets to understand how having psoriasis might make somebody more or less likely to get cancer.  

In Depth

Although epidemiology is not a field that is as well-known as others, like maths or chemistry, its results are often very well publicised and can shape how many people live their lives. The first epidemiological study was conducted in London by John Snow (not the one from Game of Thrones), who used a map of cases of ill health and interviews with local people to identify a contaminated water pump that was spreading cholera. Since this first study, epidemiology has been developed and used in a lot of different ways to improve health – from proving that smoking can be extremely bad for your health to recognising the role of mosquitos in the spread of yellow fever. Though more traditional methods are still used to quantify disease and its distribution - for example, in recent Ebola outbreaks - epidemiology has also evolved to use big data and more complex techniques, such as machine learning. 

In my research, I will be using big data to understand how having psoriasis may influence the risk of developing cancer. Although psoriasis presents as a condition of the skin, it involves chronic, systemic inflammation and this has been linked to an increased risk of cancer in other conditions, such as inflammatory bowel disease. However, attributing an altered risk of developing cancer to the inflammation involved in psoriasis is challenging due to the presence of other lifestyle behaviours, such as smoking. As it has been demonstrated that smoking is more common in people with psoriasis, it is challenging to say whether people with psoriasis develop cancer more often because of their psoriasis or because they are more likely to smoke – this is a concept known as confounding in epidemiology.

To try to understand whether people with psoriasis do develop cancer more, and whether it’s likely to be a result of their psoriasis or other lifestyle behaviours, I am analysing health data recorded by GPs and Hospitals in England. By following anonymous people with and without psoriasis through their health records, it is possible to compare the number of cancer diagnoses in each group. Having data for behaviours such as smoking then allows me to understand how these factors might be influencing any risk.

Gaining an understanding of whether people with psoriasis do develop cancer more, and what might be causing this, is vital for the current care of people with psoriasis and may also guide important future immunological research into the topic.

Going Further

To learn more about John Snow’s first epidemiological study -

To learn more about epidemiology –

To learn more about psoriasis –

Population health at the University of Manchester –