Smoking around pregnant women significantly increases the risk of the baby developing asthma, a new study suggests.
DNA scientists found correlations between altered expression of genetic code in children and fathers who smoked.
They believe this may harm the developing immune system, making it more likely for children to go on to develop the potentially dangerous respiratory disease.
Published in the journal Frontiers in Genetics, the study is significant because it is the first genetic analysis to separate distinctly babies whose mothers actively smoked during pregnancy and those whose mothers endured passive smoking.
Approximately 5.4 million are currently being treated for asthma in the UK.
Dr Chih Chiang Wu, of Po-Zen Hospital in Taiwan, where the study took place, said: “We found that prenatal exposure to paternal tobacco smoking is associated with increased methylation of certain immune genes, which alters how the genetic code is read.
“This smoking-associated DNA methylation is significantly retained from birth to six years of age and correlates with development of childhood asthma.”
The study followed 756 children up to the age of six, and included regular medical examinations and DNA testing.
Those with whose fathers smoked more than 20 cigarettes a day had roughly a 35 per cent risk of asthma, while those whose fathers smoked but fewer than 20 a day had a 25 per cent risk.
Those whose fathers did not smoke had a 22.7 per cent risk.
Babies whose fathers smoked the most showed a more than 43 per cent alteration in gene expression.
The research team said it is possible that the increased asthma risk may arise from damaged sperm pre-conception.
Previous research has shown that mothers who smoke while pregnant and breastfeeding may harm the fertility of their children.