Social epidemiologist and medical specialist in preventive medicine and public health, Gullón completed his doctorate in the Social and Cardiovascular Epidemiology group of the University of Alcalá, studying how the physical elements of the city influence social inequalities in health, a field in which he continues his academic activity. He has also been researching at the Drexel Dornsife School of Public Health and has been a professor of Epidemiology and Public Health at the Madrid campuses of St. Louis University and New York University. He is a member of the Spanish Society of Epidemiology (SEE) and the Silesia Collective.