Alternative and additional mechanisms to the hygiene hypothesis

Abstract

The rising incidence of allergic and autoimmune diseases is occurring ona background of genes selected for strong immune responses. Possiblemechanisms for selection and changed environmental factors that impacton immune response genes are discussed. Reduced exposure of infants toinfections is discussed elsewhere in this volume. Here we consider therole of delayed exposure to infections as well as additional factorsthat could promote chronic immuno-inflammatory diseases. These includechanges in the amount of food consumed, dietary composition, sleepreduction and lower energy expenditure due to reduced exercise andthermoneutrality of the built environment. Any or all of these mayresult in obesity, which is a proinflammatory state. Increases in airpollution and psychological stress and, finally, insufficiency ofvitamin D, are discussed, as these may also shift immune responsivenesstowards a proinflammatory state.