Here, we explain why it is difficult to link autism to environmental factors, and what scientists know about how the environment influences autism risk.
What qualifies as an environmental risk factor?
The term ‘environmental risk factor’ is usually understood to mean the chemicals or pollutants a person is exposed to. But scientists use a broader definition: An environmental risk factor is anything that alters the likelihood of having a condition and isn’t encoded in an individual’s DNA.
Which environmental risk factors for autism are well established?
The most widely accepted risk factors operate during gestation or around the time of birth. Various pregnancy and birth complications are associated with an increased risk of autism. These include preterm birth, low birth weight and maternal diabetes or high blood pressure during pregnancy. Scientists are not sure of the mechanisms underlying these associations.
Which proposed risk factors have been ruled out?
Despite the links between maternal immune factors and autism, routine vaccinations given during pregnancy, such as those against influenza and whooping cough, do not appear to boost autism risk.
Childhood vaccines are similarly in the clear.
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