Questions about possible impacts of environment on health can take many forms – and they can relate to the positive as well as the adverse effects.  Nevertheless, not all these questions merit an integrated assessment.  Some may be relatively simple and be better addressed by other means (see IEHIA in relation to other forms of assessment).  Others may be too general or vague to be capable of assessment.

Integrated environmental health impact assessment is most appropriate, therefore, for relatively complex issues that have the capability to affect large areas and large numbers of people.  These are sometimes described as systemic – in that they typically involve a range of different causes, deriving from different environmental, social, economic, political or technological sectors, and have many different health (and other) impacts.  Systemic issues are perhaps increasingly common in the modern world, not least because of the increased scale of technology and the ever larger imprint of society on the environment.  Obvious examples include climate change, food security and many aspects of environmental pollution. 

As this implies, relevant questions are often related to government (or inter-governmental) policies.  These are not restricted either to environmental policies, or to policies directly concerned with health.  Many other forms of policy (e.g. on energy, transport, agriculture, urban development) also have the capacity to affect health, albeit unintentionally, and thus merit integrated assessment.  Moreover, policies are not the only drivers for integrated assessments; other forces for change (such as technological developments, natural environmental changes or hazards, or demographic change) are equally relevant.   Any one of these can thus act as the motivation for assessment.