Parents who smoke are being urged not to share their bed with their baby after a survey found many did not know this raises the risk of cot death. The Foundation for the Study of Infant Deaths found a third of 428 parents polled had shared a bed with a baby.
It makes no difference where or when they smoke - if a smoker shares a bed with a baby it increases their risk of cot death even if they never smoke in bed.
Children of smokers tend to be smaller, and to have damage to their respiratory system, and so are vulnerable to the tiny risk associated with sharing a bed, which is not a factor for more robust babies.
FSID director Joyce Epstein said: "The results of this poll are worrying.
"With seven babies dying as cot deaths every week and the high proportion happening when sharing a bed - especially when parents are smokers - we must not be complacent."
Claire Jolly is a health visitor whose baby son Charlie died as a cot death in 1997.
She said: "It's fine to breastfeed your baby in bed but if you smoke at all - even if not in the bedroom - you really must protect your baby and put them in their cot to sleep."