Some of the problems that develop from urbanization are a strain on basic services, increased poverty, poor public education, sanitation problems and rising crime rates. Urbanization, which is basically rapid urban growth, also brings with it a condition referred to as "urban sprawl" in which scattered urban development results in traffic congestion, environmental deterioration and the loss of open space and parks. In many of the high-density living areas in megacities, which are cities with populations more than five million, significant portions of the inhabitants, sometimes as high as 40 percent, live in a state of environmental degradation, poor security and irreversible poverty.
Slum growth is a serious negative result of urbanization. Fueled by an influx of migrants from rural areas in search of better employment opportunities, those individuals unable to find employment or better than subsistence-level work are forced to live in squalor in areas plagued by high crime, poor schools and a heavily debilitated social infrastructure.
High concentrations of water and air pollution can become significant health problems as a result of urbanization. Heavily populated urban areas also produce a greater amount of heat and absorb more of it from the sun's energy. Cities are often warmer than rural areas, and there has been growing concern over the hazards associated with city areas that are being referred to as "urban heat islands." According to a July of 2013 report released by the Department of Economic and Social Affairs of the United Nations, the combination of population growth, environmental deterioration and increasing urbanization has the potential to cause a humanitarian nightmare in urban areas by 2050.