Public health officials have long been concerned about the effect of the environment on human health. In the nineteenth century, public health efforts in the United States were focused on controlling the spread of infectious disease, and advances in sanitation and the provision of clean water contributed to improvements in the health of the population. At the turn of the century, urban reformers adopted zoning laws and building codes to reduce the spread of disease from overcrowded conditions in central cities by lowering housing densities, as well as to separate residences from noxious commercial and industrial enterprises
