Expectant mothers who used the treatment to kill their pet's fleas were twice as likely to go on to have children with autism, Professor Irva Hertz-Picciotto, from the University of California, will tell an international meeting on the condition.
The findings will add to theories that environmental factors in combination with certain genetic factors can cause autism.
Scientists asked mothers of children with autism to detail any chemicals their offspring may have been exposed to, including insecticides, pet shampoos, and weedkillers, in the three months before conception until their first birthday.
They found that mothers of autistic children were twice as likely to report using pet shampoos which contained the pyrethrins as those who children did not have the condition.
The strongest association was in the second three months of the pregnancy, when mothers with autistic children were 2.6 times more likely than others to have been exposed to the chemical.
Widely used to control fleas, pyrethrins work by affecting the pests' central nervous system.
In laboratory tests, pyrethrins have also been found to affect a part of the brain that protects it from chemicals within the blood.
But Richard Mills, the director of research at Research Autism, called for more studies... stating "Autistic disorders are complex and it is not possible to isolate specific causes or risk factors on the basis of such evidence."
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