Eczema and Allergen Sensitization Interact to Strongly Increase Food Allergy Risk
Not all babies with early eczema are at equal risk for other allergic conditions, according to a paper published in November 2017 by the Journal of Allergy and Clinical Immunology. One-year-olds who have eczema (atopic dermatitis) and are also sensitized to one or more environmental or food allergens are at starkly greater risk for other allergic conditions at age 3, compared to babies with eczema who are not sensitized.
The term “atopic march” is used to describe a pattern in the natural history of allergic conditions, in which children who have eczema as infants, sometimes accompanied by food allergies, are more likely to have asthma and hay fever (allergic rhinitis) later in childhood. However, not all babies with eczema go on to develop other allergies.
To better understand the worldwide rise in allergy prevalence, researchers in Canada are following a cohort of children from birth to age 5. In this prospective type of longitudinal cohort study, participants are followed over time to identify factors that influence disease outcomes. The November 2017 paper tracked physician-diagnosed allergies in 2,300 children from the Canadian Healthy Infant Longitudinal Development (CHILD) cohort. Children were assessed at age 1 for eczema and for positive skin prick tests to allergens and at age 3 for eczema, food allergies, asthma and hay fever.
Adjusting for other traits that influence allergy risk, such as parental history, the relative risk of developing food allergy by age 3 is more than 4 times greater for babies who have eczema at age 1, compared to babies without eczema. Sensitization was even more strongly associated with increased incidence of food allergy. The relative risk of food allergy was more than 16 times greater for children with positive skin prick tests to at least one of ten allergens (six inhalant allergens, plus egg white, cow’s milk, peanut and soy), compared to babies with negative skin prick tests.
The combination of eczema and sensitization in early life dramatically increases food allergy risk. Compared to the reference group of children with no history of sensitization and no early eczema, the risk for food allergy by age 3 was 33-fold greater for sensitized babies with eczema. By contrast, children with eczema at age 1 who were not sensitized had a modest but statistically insignificant increase in relative risk for food allergy. These results were unchanged when children who had already developed food allergies by age 1 were excluded from the analysis.
A similar risk pattern was observed for asthma. Eczema without sensitization to allergens had no effect on asthma risk, but sensitized babies with eczema were at 7-fold greater risk for asthma, compared to the reference group. Eczema at age 1 also increased the relative risk of having hay fever or eczema two years later. Sensitized babies with eczema were at greater risk for future hay fever or eczema than were babies with eczema and negative skin prick tests, but the increases in risk were statistically significant for both groups.
Early sensitization alone, in the absence of eczema, resulted in a 13 times greater risk of food allergy at age 3, compared to the non-sensitized, eczema-free reference group. Previous research in the CHILD cohort showed that avoiding specific foods during the first year of life increased the risk of sensitization to those foods by age 1. Given the strong interaction between eczema and sensitization in enhancing risk for food allergies, these findings highlight the benefits of introducing allergenic foods early, particularly for children with eczema.