Newborns are especially vulnerable to disease if they grow up in overcrowded places and are subjected to poor hygiene, excessive noise and lack of space for recreation and study. They suffer not only from a hostile physical environment, but also from stress and other factors such as violence that such environments create.

It is important to pay attention to the special health needs of children left at home by migrants, in many cases in the care of grandparents. Some studies show that adolescents whose parents have migrated to cities tend to have a less healthy diet, become overweight and are more prone to smoking and drinking alcohol. Their conduct can be explained, in part, by the lack of parental control.

Many city residents take for granted the access to basic public services such as drinking water supply, housing, solid waste disposal, transportation and healthcare.

For the poor, however, these are either deficient or non-existent. Instead, people living in poor neighborhoods usually get an extra dose of environmental pollution, because many industries tend to cluster in outlying areas where regulations are comparatively lax. Unemployment, poverty and crowded living conditions contribute to violence, substance abuse and mental illness.

In cities, motor vehicles are a big source of air pollution. They cause pedestrian injuries and fatalities, too. The pollutants that motor vehicles emit, particularly nitrogen oxide, hydrocarbons, ozone and particulate matter, account for a substantial proportion of air pollution in cities and have a serious impact on health. Some cities such as Wuhan, Qingdao and Hangzhou have implemented new anti-pollution and anti-congestion measures, which should be followed by other cities.

Crowded urban neighborhoods, combined with poor sanitary conditions and inadequate waste removal, create conditions for the spread of infectious diseases such as pneumonia, TB and cholera. Inadequate sanitation is an important risk factor for diarrheal and parasitic diseases.

Given the serious effects that urbanization can have on health, it is essential to include health considerations into policymaking. Since the poor and migrants suffer many of the negative effects more acutely, it is important to assess their needs properly. More efforts should be made to devise prevention policies in industries where migrants are concentrated.

Cities are magnets that attract migrants for the opportunities they offer but they must provide a safe and stable environment for people to prosper. As Herbert Girardet, an expert on urban sustainability has said: "If we are to continue to live in cities, indeed if we are to continue to flourish on this planet, we will have to find a viable relationship between cities and the living world - a relationship not parasitic but symbiotic, or mutually supportive."

The author is an international public health consultant and has penned the Environmental Impact on Children's Health, a book published by the Pan American Health Organization, the regional office of the World Health Organization.

(China Daily 05/26/2011 page9)