According to a report in the British Journal of Cancer sperm may be damaged by the father smoking, resulting in genetic mutations being passed on.
The team that carried out the research looked at the smoking habits of the parents of 2,587 children who died of cancer and compared then to a similar size control group.
"Maternal daily consumption of cigarettes and paternal use of pipes or cigars were unimportant, but there was a statistically significant trend between paternal consumption of cigarettes and the risk of childhood cancer. About 14 per cent of childhood cancers in this series could be attributable to paternal smoking," says the report.
It adds: "The smoking of cigarettes by mothers can, with some confidence, be excluded as an important risk factor for the generality of childhood cancer."
It is the toxic elements of the inhaled cigarette smoke which are suspected of causing the damage: "Cigarette smoke contains a high concentration of oxidants ... If unchecked, oxidants can cause considerable damage to DNA and these reactive mutagens have been shown to be involved in a variety of physiological processes, including cancer."
At what stage the sperm may be damaged is not known. The complete spermatogenesis process takes 74 days and at any time during that period it could be mutated, but earlier smoking might also be implicated.
One of the authors, Dr Tom Sorahan of the Institute of Occupational Health at Birmingham University said yesterday: "The theory based on the latest research is that the DNA is damaged by the smoke. We know that smoking can cause cancer in many parts of the body and the toxic chemicals in the smoke are circulating throughout the body. Latest work shows that it is getting to the sperm and damaging it."Reuse content