Air pollution and sudden unexpected death in infancy: a critical review of potential neurotoxic mechanisms

Sudden unexpected death in infancy (SUDI) is defined as the sudden death of an infant under one year of age. If a complete investigation (including a review of clinical history, an examination of the death scene and a full autopsy) fails to identify a specific cause, the death is classified as sudden infant death syndrome (SIDS). 1 Some risk factors associated with SIDS are well known, such as infant sleeping position (the prone position being particularly risky), exposure to cigarette smoke, sleeping practices, sex (as the incidence is higher in boys), premature birth, and genetic predispositions. 2 , 3 One of the main hypotheses explaining SIDS is the so-called “triple risk model” of Filiano and Kinney. 4 According to this model, death results from the coincidence of three factors: 1) vulnerability (prematurity, intrauterine growth restriction, genetic abnormalities or prenatal smoke exposure); 2) a critical developmental period, with approximately 90% of deaths occurring in the first six months of life; and 3) an external stress factor, such as prone sleeping position, inadequate sleeping environment, exposure to tobacco smoke, etc. 3 , 4 , 5 , 6 Environmental exposure may play a particularly important role, both by increasing vulnerability and by acting as a trigger. Although most studies focus on SIDS, underlying biological mechanisms may extend beyond this category and also play a role in some deaths classified as explained. From this perspective, environmental exposures, including air pollution, could contribute to SUDI more broadly.