Early exposure to tobacco smoke causes asthma and allergy

Babies exposed to cigarette smoke before birth or during the first months afterwards run a greater risk of developing asthma and allergy. This according to a doctoral thesis from the Swedish medical university Karolinska Institutet.

It is a well known fact that babies are harmed by tobacco smoke in numerous ways, but it has always been difficult to separate the effects of the mother smoking during pregnancy and passive smoking after birth. Dr Eva Lannerö's doctoral thesis now provides new detailed knowledge on how exposure to tobacco smoke early in life influences the risk of developing allergy and asthma respectively.

The thesis, which is based on the so called BAMSE study, shows that smoking during pregnancy increases the chances of the child developing asthma. The study showed that children of mothers who had smoked while pregnant ran double the risk of developing asthma before the age of four. There was also a clear correlation between the number of cigarettes smoked and the risk of developing asthma.

Her thesis also shows that passive smoking in early childhood increases the risk of allergy. Four-year olds who were exposed to tobacco smoke when they were two months old had IgE antibodies (allergy antibodies) against one or more allergens in the blood more often than their coevals from non-smoking homes. The strongest correlation was observed for antibodies against cat allergens, which were twice as common in these children.

"This is particularly worrying as cat allergens are almost everywhere and are hard to avoid," says Dr Lannerö. "We can't say how many, but some of these children will definitely develop chronic asthma."

Dr Lannerö's studies also show that smoking during pregnancy is least common amongst the higher educated. Of the 4,000 interviewed mothers, 7 per cent of those with university-level education said that they had smoked while pregnant, as opposed to 20 per cent of those who had opted out of tertiary or secondary education. The data applies to mothers of children born between 1994 and 1996.

The BAMSE study is a project in which 4,100 Swedish children born between 1994 and 1996 have been monitored from birth in order that scientists can learn more about the impact of different environmental factors on the development of childhood allergy.

Thesis: 'Parental smoking, wheezing and sensitisation in early childhood', Eva Lannerö Institute of Environmental Medicine (IMM), Karolinska Institutet.