An important question is how these different influences relate to each other in their net effect on health.  The effects of air pollution, for example, might be weakened by social capital and green space, and the health consequences of air pollution might be worse in neighborhoods that are unsafe. Long-term health effects from air pollution include heart disease, lung cancer, and respiratory diseases such as emphysema. Air pollution can also cause long-term damage to people's nerves, brain, kidneys, liver, and other organs. Some scientists suspect air pollutants cause birth defects