A chemical commonly found in pet shampoo may increase the risk of autism in children, a new study has found.
The study of how environmental factors influence the developmental disorder found that expectant mothers who used the shampoos to kill their pet's fleas were twice as likely to go on to have children with autism.
The findings, from the Childhood Autism Risks from Genetics and the Environment study, which is funded by the US National Institutes of Health, increase the possibility that chemicals called pyrethrins found in pet shampoos and flea sprays are linked to a raised risk of autism.
However, scientists behind the research stress that the findings remain preliminary.
Scientists asked mothers of children with autism to detail any chemicals their kids may have been exposed to, including insecticides, pet shampoos, and weedkillers, in the three months before conception until their first birthday.
Results showed that mothers of autistic children were twice as likely to report using pet shampoos, which contained the pyrethrins as those whose children did not have the condition.
"Mothers of ASD children were twice as likely to report using pet shampoos for fleas or ticks during the exposure period as compared with control mothers," Times Online quoted Irva Hertz-Picciotto, of the University of California-Davis , as saying.
"The strongest association was during the second trimester, but risk was elevated for use in other time windows as well.
"It is possible that mothers of typically developing children tended to forget about their use of pesticides around the home, which could have biased the results.
"Nonetheless, the higher self-reported use of pet shampoos by mothers of children with ASDs raises concern about the safety of these products," she added.
Hertz-Picciotto further said that the findings would add to theories that environmental factors together with certain genetic factors can cause autism.