Infectious diseases have a specific, ethiological cause, e.g. a microbe such as tuberculosis caused by Mycobacterium tuberculosis. However, most people exposed to TB does not develop the disease. What determines this may be poverty, weakening of the person by other diseases or smoking and alcohol. So-called life-style diseases are (also) determined by the way you live, and include prevalent non-communicable diseases such as type 2 diabetes and cardio-vascular diseases, but besides of risk factors such as smoking and drinking or over-eating, the living conditions matter equally and sometimes more. The environment, climate changes, urbanization, socio-economic factors all impact health and disease. When an individual grows older, patterns of his/her diseases changes: the same applies when a society grows ‘older’.

Previously infectious diseases previously caused the majority of ill-health and premature death globally, but in high- and middle-income countries during the 20.th century infectious diseases – with the exception of HIV – declined. Introduction of hygiene and discovery of microbes and later vaccines an antibiotics contributed to the decline, but changing living conditions with better housing, nutrition, water and sanitation were the main drivers of infectious diseases’ decline.