Sex hormones, medications, certain metals such as lead, pesticides, and chemicals used to make plastic hard or pliable have long been suspected of having a role in autism.
They have not been proven to cause autism, but these are known to trigger or worsen other health problems, including some that affect the brain.
Many studies have shown that chemical exposures during development in the womb can have much more serious health effects than the same exposures would in adults.
A large 2014 study investigated the connection between autism and genital malformations using health insurance claims from almost a third of the U.S. population.
Like autism, genital malformations are increasing: cases of undescended testicle(s) increased 200% between 1970 and 1993, and the percentage of boys born with a deformity of the penis known as hypospadia doubled.
Many studies have shown that these malformations are more common among children whose mothers have high levels of chemicals that affect the hormones in their bodies, such as phthalates which are found in cleaning products, medicines, and personal care products like shampoos and creams (see our article on phthalates.)
The link between these chemicals and genital malformations has surfaced in other studies, particularly those involving women in professions (chemists, health care workers, housekeepers) that require working daily with these chemicals.[
The 2014 study based on insurance claims found that boys born with genital defects were much more likely to be diagnosed with autism.
Boys with autism spectrum disorders (ASD) were 5.5 times more likely to be born with genital malformations than males without ASD.
However, there was no connection between genital malformation and intellectual disability.
A similar pattern was observed for girls, but the connection wasn’t as strong. No one knows why but, ASD is 5 times more common in boys than girls.
As found in previous studies, the children with autism in this study were more likely to live in cities and be from families with higher income.
For every additional $1,000 in income above the country average, the rate of autism went up by about 3%. A similar trend was seen with measurements indicating how urban a household’s location was.
However, city-living and wealth had a much weaker connection to autism than genital malformations.
While this study doesn’t prove that exposures to chemicals in our environment cause autism, it suggests that whatever is behind the increase in genital malformations could be behind the increase in autism.
Researchers need to continue to investigate the possibility that environmental exposures are contributing to autism.