The increase in autism prevalence is predominantly due to improved and broader diagnostic criteria, increased awareness, and more frequent and earlier diagnoses rather than a true rise in underlying autism traits. Changes in diagnostic manuals have expanded the definition of autism to include individuals with milder symptoms who were previously undiagnosed or diagnosed differently. Greater public and professional awareness, reduced stigma, and enhanced screening tools have also contributed to more diagnoses, including in adults and females who were previously overlooked. Besides diagnostic factors, some increase may be linked to environmental and genetic factors, but these play a smaller role compared to diagnosis changes. Known environmental risk factors during pregnancy include infections with fever, exposure to air pollution, and complications such as prematurity. Older parental age and better survival of premature babies also contribute somewhat to observed rises. However, discredited theories like vaccines causing autism have no scientific support. In sum, the observed rise in autism diagnoses reflects mostly changes in how autism is recognized and diagnosed rather than a real increase in the condition's frequency in the population.
