Campaigners have called for action to protect children after research highlighted a link between illness and pesticide use in or near schools.
Pesticides are linked to health problems
Scientists found the rate of illnesses linked to pesticides and similar chemicals rose sharply between 1998 and 2002 in US schools.
Most of the 2,593 patients affected had mild illnesses, but some were more serious, and a few severe.
The study is published in the Journal of the American Medical Association.
Exposure to pesticides can cause rashes, sore throats, burning eyes, blisters, headaches and nausea as well as potentially more serious long term effects.
The scientists, from the National Institute for Occupational Safety and Health and the US Centers for Disease Control and Prevention in Cincinnati, examined 406 cases in detail.
They found two-thirds were associated with pesticides used in schools, and a third with chemicals drifting into schools from nearby farms.
The scientists recommended measures to improve the use of pesticides in schools, reduce pesticide drift and set up pesticide spray "buffer zones" around school buildings.
The UK Pesticides Campaign called for immediate action to protect the public, and the replacement of chemicals with natural methods of pest control.
Georgina Downs, who heads the Campaign, said: "Children are particularly vulnerable to the effects of pesticide exposure because their bodies cannot efficiently detoxify and eliminate chemicals, their organs are still growing and developing.
"I continue to receive reports of illnesses in children attending schools where pesticides are used, especially schools surrounded by crop fields that are repeatedly sprayed, throughout every year, with mixtures of pesticides.
"Pesticides have been sprayed around schools, peoples homes, offices and other places of human habitation for decades.
"No adequate or appropriate risk assessments have ever been undertaken either in the UK or internationally regarding the long-term exposures of rural residents and communities, including children and employees attending schools where pesticides are used."
The Royal Commission on Environmental Pollution is due to publish a report on "bystander" exposure to pesticides in September.
Ms Downs has gone to the High Court challenging a decision by the Department of Environment Food and Rural Affairs (Defra) not to introduce no-spray zones around agricultural land.
The application is on hold pending publication of the Royal Commission's report.
A Defra spokesperson said the latest study would be put to the Advisory Committee on Pesticides and the Pesticides Safety Directorate.
"There is already a detailed system of risk assessment employed to ensure that the particular effects of pesticides on children are properly taken into account."
She also stressed there were significant differences in the way pesticides were used in the US and the UK.
Peter Sanguinetti, of the Crop Protection Association, said: "Our industry is fully committed to complying with the robust regulation by the Pesticide Safety Directorate which ensures that our products are safe when used correctly.
"Every label has clear instructions which must be followed."