Professor David Strachan joined St George's as a senior lecturer in 1990, following undergraduate education at Cambridge and Edinburgh universities, vocational training in general practice, and four years of epidemiological research at the University of  Edinburgh and the London School of Hygiene and Tropical Medicine.

November 2019 marks the 30th anniversary of publication of his most influential paper, proposing what is widely known as the "hygiene hypothesis" for allergic disease. This early contribution has been cited more than 2800 times.

In 1999, he was awarded the European Respiratory Society prize for paediatric respiratory research in Europe (jointly with Professor Derek Cook, also from St George's), for systematic reviews of the effects of parental smoking on health of children. This work formed an important part of the evidence base for recent legislation, in several countries, banning smoking in cars when children are present.

Professor Strachan was a founder member of the International Study of Asthma and Allergies in Childhood (ISAAC) which completed the first global assessment of geographical variations and time trends in the prevalence and severity of childhood asthma, rhinitis and eczema. He served on the ISAAC Executive for 20 years until the completion of the study at the end of 2012. From 2012, ISAAC evolved into the Global Asthma Network (GAN) as a joint initiative with members of the International Union Against Tuberculosis and Lung Disease. Professor Strachan continues as a member of the GAN Steering Group.

These three areas of research, combined with more recent national and international collaborations in genetic epidemiology, contributed to his inclusion in the Thomson Reuters (later Clarivate Analytics) List of Highly Cited Researchers for five years from 2014 to 2018.

Professor Strachan was Associate Editor of Thorax from 1996 to 2006 and has served on a number of advisory committees of the UK Department of Health, the Medical Research Council, the Wellcome Trust and the National Institute for Health Research. He was Chair of Examiners for the UK Faculty of Public Health from 2006 to 2009 and continued until 2012 to lead development of the Part A (written) Faculty of Public Health examination.

Professor Strachan led the development of community health (later renamed population health) at St George’s as head of department, research centre or research institute from 2004 to 2016. From 2014 to 2017, he served on the Council for St George's University of London as an elected staff member. Since 2017 he has been working part-time, combining undergraduate and postgraduate teaching with continuing research into the epidemiology of allergic, respiratory and cardiovascular diseases.

Professor Strachan’s research career started in the mid-1980s when he studied the effect of indoor dampness and mould growth on asthma in childhood. In 1989 he published a short paper in the British Medical Journal which speculated that infections might protect against allergic diseases. This article has subsequently received more than 2800 citations and has been dubbed the “hygiene hypothesis”.

During the 1990s, Professor Strachan studied the effects of outdoor air pollution and indoor air quality on respiratory disorders, and the possibility that chronic infections might increase the risk of cardiovascular disease. He continued to research specific aspects of the “hygiene hypothesis” for allergic diseases.

During the 2000s, his research explored lifecourse influences on health in the British 1958 birth cohort, and he led the development of a nationally representative DNA collection, based on this cohort, for use in genetic epidemiology. This led to numerous international collaborations investigating combinations of genetic and environmental influences on disease, particularly respiratory and allergic conditions, and cardiovascular risk factors.

Professor Strachan was a member of the UK Biobank Protocol Development Committee in 2002-2003. Following completion in 2010 of the first round of fieldwork in this national study of over 500,000 adults, he investigated how well measurements of lung function predict subsequent mortality and non-fatal illnesses, particularly in lifelong non-smokers. He was co-investigator on the first genetic study in UK Biobank (UK BiLEVE) which investigated the interaction between genetic variants and smoking habits in determining lung function.

Currently, Professor Strachan is collaborating with colleagues at St George’s and Kingston Universities to automate the processing of retinal photographs from UK Biobank and explore whether the size or shape of retinal blood vessels may predict cardiovascular complications.

Throughout his 30-year research career at St George’s, Professor Strachan has been actively involved in international collaborations. He was a founder member of the International Study of Asthma and Allergies in Childhood which expanded over 20 years (1992-2012) to form a global network of over 300 study centres. He developed a close liaison with the ISAAC Data Centres at the University of Auckland, New Zealand and University of Ulm, Germany. From 2007 to 2017 he provided mentorship and supervision of the ISAAC group in Ulm, following the untimely death of the institute director there. From 2012, ISAAC evolved into the Global Asthma Network (GAN), on which he continues to serve as a steering group member.

Professor Strachan has published more than 450 peer-reviewed journal papers. He has a lifetime h-index of over 100 (having published more than 100 papers each of which has been cited at least 100 times). More than ten of these papers have been cited at least 1000 times. In five successive years (2014 to 2018), he was included in the Thomson Reuters (later Clarivate Analytics) List of Highly Cited Researchers. This is a list of researchers worldwide who are ranked among the top 1% most cited for their subject field and year of publication.

Professor Strachan contributes to undergraduate teaching and assessment in statistics, epidemiology and public health. He contributes to postgraduate (masters-level) teaching in critical appraisal and genetic epidemiology. He has supervised six internal PhD students to successful completion, and is currently co-supervisor for one external PhD student. He represents non-laboratory research at St George’s within the steering group of the MRC-funded Doctoral Training Partnership with the London School of Hygiene and Tropical Medicine.