Secondhand smoke may raise child allergy risk

NEW YORK (Reuters Health) - Young children who were exposed to cigarette smoke as babies may be more likely to suffer certain allergies, a new study suggests.

Experts have known that exposure to secondhand smoke either prenatally or early in life can raise a child's risk of developing asthma symptoms. But the evidence regarding allergies in general has been mixed.

In the new study, Swedish researchers found that 4-year-olds who had been exposed to parents' smoking during early infancy were at greater risk of allergies to indoor allergens like dust mites and cat dander. They were also at greater risk of food allergies.

It's possible that secondhand smoke triggers inflammation in the lining of young children's airways, which may sensitize them to allergy-triggering substances, according to the researchers, led by Dr. Eva Lannero of the Karolinska Institute in Stockholm.

She and her colleagues report the findings in the medical journal Thorax.

The study included more than 4,000 families with infants born between 1994 and 1996. Parents were asked whether either of them smoked when the child was 2 months, 1 year or 2 years old. At the age of 4, the children had their blood tested for antibodies to a range of common allergens, such as cat dander, dust mites and mold, as well as foods such as milk, eggs and wheat.

The researchers found that children who'd been exposed to cigarette smoke at the age of 2 months were 28 percent more likely to have antibodies to either an indoor air allergen or a food allergen.

In particular, their odds of being sensitized to cat dander were double that of children with no secondhand smoke exposure at 2 months of age. And they were nearly 50 percent more likely to have antibodies to food allergens.

The findings, according to Lannero's team, support the theory that early damage to the mucous membranes lining the airways may make children more sensitive to allergens. They also offer parents yet another reason to keep their children away from secondhand smoke.

SOURCE: Thorax 2007.