Early Infections = More Allergic Disease?

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By Jennifer Hahn

Previous studies have consistently shown that the likelihood of allergic diseases decreases as the number of siblings increases. Why this is the case is not clear. Researchers evaluated whether having infectious disease early in life (in the first six months) would be related to lower rates of atopic dermatitis (a type of eczema associated with allergies) at 18 months.

The sample of participants in the study included 24,341 mother-child pairs in Denmark. More than half (54%) of the children had at least one infectious disease before six months of age. The majority (85%) had a cold, with slightly more boys than girls having had an infectious disease.

About 10% of the children had atopic dermatitis by 18 months of age, with more boys (54%) than girls (44%) having had it. The children who had at least one infectious disease before six months were more likely to have atopic dermatitis. This was especially true for girls.

Factors that were associated with a decreased risk of atopic dermatitis included living on a farm, greater number of siblings, owning a pet and attending day care early. The findings support the idea that exposure to germs early in life may help protect against allergic diseases. However, this is not true for early infections.

Source: Benn, C. S., et al., April 2004, Cohort study of sibling effect, infectious diseases, and risk of atopic dermatitis during first 18 months of life. British Medical Journal (BMJ).

© Jennifer Hahn

Dr. Jennifer Hahn is the editor of The Thinking Parent, a quarterly publication reviewing research of interest to parents: child development and parenting, pregnancy and childbirth, physical health, mental health and education. With more than 12 years of experience in research at the Johns Hopkins School of Medicine, Dr. Hahn received her Ph.D. from the University of Maryland Baltimore County and completed her residency at the University of Virginia Health Sciences Center. She is the mother of two daughters.