Trump’s post also drew criticism due to the fact RFK Jr has previously endorsed debunked theories that vaccines cause autism.

But a growing body of recent research suggests other external factors cannot be dismissed as conspiracies.

Some studies have shown growing pollution and chemical contamination in food and water may allow toxins to infiltrate the bloodstream of pregnant mothers and travel to the brain of the developing fetus, causing inflammation that impairs nerve signals that lead to autism.

Some experts have also speculated a surge in pesticide use may also be responsible for lower IQs and delays in children.

Additionally, more babies are surviving being born prematurely than in decades past, making them more vulnerable to developmental delays and autism.

This could be related to the fact women are having children older than ever, or other changes to do with parents, such as the rising prevalence of obesity.

However, the increased prevalence of autism may not be a uniquely American phenomenon.

In the UK, a record 200,000 Brits in 2024 were reportedly waiting to be screened for autism, a nine-fold increase from 2019, data from the country’s National Health Service shows.