A new analysis of existing research finds that kids exposed to pesticides indoors are at higher risk for childhood cancers.

The study, based on data mainly from North America, Europe and Australia, suggests that policies should be developed to limit children’s exposures at home and school to insect killers, researchers say.

“When you apply pesticides so close to where kids are and they spend so much time in the household, I’d really be concerned about their exposure,” said Chensheng Lu, the senior author of the analysis from the Harvard T.H. Chan School of Public Health in Boston.

The researchers write in Pediatrics that children can be exposed to pesticides when they play on treated surfaces and then put their fingers in their mouths.

Unlike adults, children may not be able to break down or excrete some of the chemicals used in pesticides. Reports show children had respiratory, stomach, nerve and hormone problems tied to pesticides, Lu and colleagues add.

In the same issue of the journal, researchers from Italy published a report of a seven-month-old child dying after repeated exposure to massive amounts of a household insecticide.

“I think that case highlights the acute effects of insecticides,” Lu said. “The blood cancers highlight the risks of chronic exposure.”

For the new study, Lu’s team looked at published research on childhood exposures to pesticides both indoors and out, and any associated cancers. Sixteen studies were included in the final analysis, each looking at samples of a few hundred to a few thousand children. The studies looked at exposure both to professionally-applied pesticides and to household bug sprays and weed killers.

Overall, childhood exposure to indoor insecticides was linked to a 47 per cent increased risk of childhood leukaemia and a 43 per cent increased risk of childhood lymphomas, which are cancers of the lymphatic system.

The researchers also found a slightly increased risk of childhood cancers with the use of outdoor herbicides, or weed killers, but the association was only significant for leukaemia.

The link between outdoor exposure and childhood cancers was not as strong as for indoor exposure, because people tend to spray more pesticides indoors, Lu said.

More research is needed to determine how exposure to pesticides may be linked to childhood cancers, the researchers write. Lu cautions, however, that parents should keep in mind that many pesticides are meant to be deadly to insects and pests.

“Those chemicals have lethal potencies,” he said. “Why would people want to spray so close to their kids?”