But experts tell WebMD that the evidence linking insecticides to leukemia in kids remains inconclusive.
In the latest study, researchers compared exposures to a variety of pesticides, as recalled by the mother, among children with leukemia and those without the disease.
They concluded that the risk of developing acute leukemia was almost twice as high in children whose mothers reported using insecticides in the home while pregnant and when their children were small.
Use of insecticidal shampoos to treat head lice and exposure to garden insecticides also appeared to roughly double a child's risk of developing leukemia.
Head Lice Link Preliminary
Epidemiologist Florence Menegaux, MD, PhD, led the research team. She says the head lice shampoo findings, especially, should be interpreted with caution because hers is the first study to link insecticidal shampoos to childhood leukemia.
American Cancer Society (ACS) spokesman Len Lichtenfeld, MD, agrees that the study's findings must be replicated before any conclusions can be made.
"We do not believe that there is anything in this study that should deter parents from treating their children with these shampoos," he tells WebMD.
Previous, similarly designed studies have suggested a link between prenatal and postnatal indoor pesticide exposure and childhood leukemia, however.
"People need to be aware that while it is not conclusive, the evidence that this is a potential risk is certainly there," Menegaux says. "Six studies before this one came to the same conclusion."
Menegaux's study included 280 children with newly diagnosed leukemia and 288 children without the disease.
Interviews were conducted with the mothers of all of the children. The mothers were asked about both parents' work history, the use of insecticides in the home and garden, and the use of head lice shampoos.
The findings are published in the latest issue of the journal Occupational and Environmental Medicine.
Lichtenfeld characterized the evidence linking pesticide exposure to childhood leukemia as "intriguing and deserving of further study."
But even if the association is confirmed, he says, it is not likely that it is a strong one.
"When (environmental) exposures strongly influence risk it is pretty obvious, like the link between tobacco and lung cancer" he says, pointing out that the risk of developing lung cancer is up to 90 times greater for a two-pack a day, long-term cigarette smoker than for a nonsmoker.
Little is known about the causes of childhood leukemia. Cancer treatment with chemotherapy and radiation therapy is known to increase risk, and children with Down syndrome are 15 times more likely to develop leukemia than other children, according to the ACS web site.
In addition to insecticide exposure, studies have suggested that heavy alcohol consumption by a mother during pregnancy, maternal smoking and contraceptive use, and other environmental risks may increase a child's leukemia risk. But the ACS concludes that none of these has been conclusively linked to leukemia in children.