Chemicals found in pet shampoos may be linked to a raised risk of autism, a study of how environmental factors influence the developmental disorder has suggested.

Mothers who used pesticide-based shampoos to wash their pets while pregnant were twice as likely to have a child with an autistic spectrum disorder as those who did not, according to early results from a US research team.

The findings, from the Childhood Autism Risks from Genetics and the Environment study, which is funded by the US National Institutes of Health, raise the possibility that chemicals called pyrethrins found in pet shampoos and flea sprays are linked to a raised risk of autism. Scientists behind the research emphasise that the findings remain preliminary.

Mothers of autistic children may be more likely to remember their use of chemicals than are mothers whose children develop normally.

The study asked 333 mothers of children with autistic spectrum disorders (ASDs) and 198 mothers of typically developing children to fill in questionnaires about their exposure to environmental chemicals, from three months before they became pregnant to their babies' first birthdays. Irva Hertz-Picciotto, of the University of California-Davis will present preliminary findings today at the International Meeting for Autism Research in London.

“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,” she said. “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.”

It is accepted widely that autism is heavily influenced by genetics. Environmental factors may add to the risk.

Times Recommends

• Baroness Ashton: EU couldn’t make it up
• The other belles de nos jours
• Why too much of a good thing is bad for you