The World Health Organization estimates that about one-quarter of diseases worldwide are due to environmental factors. Children whose bodies have not yet developed adequate defences are particularly at risk.
Industrial plants, traffic and heating systems release harmful substances into the air we breathe. These are absorbed by the body and can contribute to the development of cancers and allergies, as well as respiratory, heart and circulatory diseases. This reduces average life expectancy, especially among people living in the big cities.
It is in big cities that vehicules are a particular problem, especially when sunlight reacts with exhaust ingredients to create a layer of choking smog. Increasing noise pollution is another problem associated with cities. Not only does it cause premature hearing difficulties, but it also results in a build-up of stress hormones which raises blood pressure, adding to the risk of heart attacks.