This chapter summarises the evidence on three early risk factors for autism identified by the lay epidemiologists of Chapter 7: being the child of older parents, being born prematurely and living in areas with high levels of air pollution. It considers how plausible each may be in explaining even a tiny proportion of the rise in autism diagnosis since 1990 in higher-income countries. Numerous studies have identified a link between older parenthood and an increased risk of autism, most probably because of spontaneous genetic mutations in the eggs and sperm of older parents. However, older mothers are also at increased risk of giving birth prematurely, or by Caesarean section, and having babies with low birth weights, all of which are associated with increased rates of autism. The effects of poor air quality are as difficult to quantify as they are potentially far reaching. Rodent studies have shown that fine particulates can cross the blood–brain barrier and induce structural and physiological damage; however, given that autism is primarily framed through impairments in social communication, autistic advocates have questioned the extrapolation of such studies to humans. Two of the three risks considered seem plausible candidates. The chapter concludes that a true distinction between what is ‘real’ and what is ‘artefactual’ is not possible.