A child whose grandmother smoked while pregnant has double the normal risk of developing asthma, it has been claimed.

Researchers found evidence that the harmful effects of tobacco can pass down the generations for decades.

A grandmother's smoking coul d have an impact on her grandchild, even if the child's mother appeared to be unaffected.

Scientists from the Keck School of Medicine at the University of Southern California in Los Angeles, USA, questioned the parents of 908 children about their smoking habits.

The study showed that children whose mothers smoked while pregnant were one-and-a-half times more likely to develop asthma early in life as children whose mothers did not smoke.

Children whose grandmothers smoked while pregnant were more than twice as likely to become asthmatic as those whose grandmothers did not. The risk was nearly doubled even if a child's mother did not smoke, but the grandmother did.