One of the first things many people do when diagnosed with cancer is to switch to organic food in the belief that pesticides or chemicals may have contributed to the illness.

A number of epidemiological studies have been looking at the effect of pesticides on cancer, according to Dr Patrick Corley, of Cancer Research Ireland, part of the Irish Cancer Society. But these studies are "ongoing and inconclusive". Still, he recommends switching to organic food where possible. "As part of a balanced diet it is sensible to consume a diet that is rich in fresh fruit and vegetables, and low in products of animal origin. This is of benefit for heart disease as well as cancer," he says.

Dr Corley also recommends avoiding the heating of food in plastic containers, or eating food that has been stored in plastic containers for long periods. This is because organic compounds, which are thought to play a role in some cancers, can leech from containers into food.

If some doctors had their way, all fruit and veg sprayed with fungicides, pesticides or other chemicals would be labelled as such. The Irish Doctors' Environmental Association (Idea) has called on the Food Safety Authority to introduce this compulsory labelling system. Dr Liz Cullen, co-founder of Idea, says while certain chemicals may be safe on their own, we don't know how they react with other chemicals in the environment.

Idea is also concerned that there is no register logging illness due to pesticide exposure. "This is really unacceptable. The Department of Health should have a system in place. People say there are no ill-effects but nobody is checking, so how do we know?" Dr Cullen says.

• For a list of known or suspected cancer-causing agents, see www.cancer.ie/cancerInfo/factors.php from the Irish Cancer Society