– Here's something else not to like about lice, mosquitoes, and fleas. An insecticide used to kill them—pyrethroids—might be linked to behavior issues in children as young as 6, a French study suggests. The researchers, noting the effects the chemical had on the nervous systems of insects, wondered how it affected humans, notably children. They tested the urine of about 300 pregnant women and, six years later, their children, according to the study published in Occupational & Environmental Medicine. Children with the highest levels of pyrethroids in their urine were three times more likely to have behavioral problems than kids with lower levels. The problems might be external (kids being defiant or disruptive) or internal (a reluctance to ask for help) depending on the specific type of pyrethroid they were exposed to, the study said. "The pesticide class studied are considered 'safe' pesticides and this study is cause for concern as to how safe it really is," says a child psychatrist at Lenox Hill Hospital in New York City who reviewed the findings, per HealthDay News. But he cautions that the study finds only a correlation, not cause and effect. Along those lines, a doctor at Johns Hopkins characterizes the study as preliminary and says it should be followed up by further research, reports Yahoo. Still, a pediatric behaviorialist not involved with the research recommended that pregnant women use "common sense" when using insecticides and look for products that don't contain pyrethroids. (In an awful story out of Massachusetts, police say a homemade lice remedy proved fatal for a girl.)