Alternative And Additional Mechanisms To The Hygiene Hypothesis

The rising incidence of allergic and autoimmune diseases is occurring on a background of genes selected for strong immune responses. Possible mechanisms for selection and changed environmental factors that impact on immune response genes are discussed. Reduced exposure of infants to infections is discussed elsewhere in this volume. Here we consider the role of delayed exposure to infections as well as additional factors that could promote chronic immuno-inflammatory diseases. These include changes in the amount of food consumed, dietary composition, sleep reduction and lower energy expenditure due to reduced exercise and thermoneutrality of the built environment. Any or all of these may result in obesity, which is a proinflammatory state. Increases in air pollution and psychological stress and, finally, insufficiency of vitamin D, are discussed, as these may also shift immune responsiveness towards a proinflammatory state.