Chemicals in head lice treatments and dog tick sprays could lead to behavioural problems in young children, research suggests.
Pregnant women exposed to pyrethroids – a group of synthetic chemicals used in common pesticides – were more likely to have children who develop social behaviour problems by the age of six, a study found.
Pyrethroids are commonly used in crop insecticides but are also used to treat humans with head lice and scabies, and are sometimes used in mosquito repellents.
They are also used in products designed to rid pets of fleas and ticks.
The chemicals were developed by British scientists in 1960s as a safe alternative to organophosphates.
But the new research, by French academics at the University of Rennes, suggests they may not be as safe as previously thought. However, other scientists were sceptical of their findings – and the researchers themselves were cautious.
The chemicals work by damaging the nerves of insects – and the researchers suspect this action may also affect the development of a child’s brain.
The researchers, whose work is published in the BMJ journal Occupational & Environmental Medicine, tested the urine of 3,421 women who were between six and 19 weeks pregnant, measuring the levels of five pyrethroid metabolites.
Six years later, they went back and assessed the children of 287 women who had taken part in the initial study. Psychologists visited the children at home to carry out behavioural assessments.
The scientists found that women who had been exposed to high levels of pyrethroids were more likely to have children with ‘internalising’ behaviours, which include fearfulness and social withdrawal.
The scientists also tested the urine of the children themselves, and those with the highest levels were about three times as likely to display abnormal behaviour.
This included internalising behaviour and ‘externalising’ behaviour, such as aggression and bullying.
This researchers stressed their study was merely observational – and no solid conclusions could be drawn about cause and effect.
And they said accurately assessing pyrethroid exposures is notoriously difficult because the chemicals are cleared from the body in just a few days. But they suspect the chemicals might alter neurochemical signalling in the brain, altering a child’s development.