By Roberta Attanasio
The frequency of allergies in children keeps rising rapidly worldwide, but it’s not clear why. However, it is acknowledged that developing even one type of allergy early in life is almost like turning on a switch—it can start children on a path to more. “The progression of skin allergies to asthma and allergic rhinitis is called the allergic or atopic march. Atopic dermatitis is an itchy, inflammatory skin allergy that, before 1960, affected fewer than 3% of children; by the 2000s it had increased to around 20%. A child with atopic dermatitis is more likely to develop other allergic conditions or symptoms. For example, about 70% of people with severe atopic dermatitis have asthma, whereas in those without atopic dermatitis, only about 8% have asthma—a nearly 9-fold difference.”
According to the American Academy of Allergy, Asthma & Immunology, atopy refers to the genetic tendency to develop allergic diseases such as allergic rhinitis, asthma and atopic dermatitis (eczema). Atopy is typically associated with heightened immune responses, more specifically with excessive IgE production in response to common allergens, especially inhaled allergens and food allergens.
Atopic diseases (eczema, asthma and rhinoconjunctivitis) are clinical syndromes each defined by a group of symptoms and signs. Not all children with atopy will have atopic disease or develop symptoms after exposure to an allergen. Both genetic and environmental factors determine the development of atopic disease.
Now, results from a new study show that there is a significant association between multiple prenatal and early life exposures to indoor pollutants and the degree of allergic sensitivity in 2 year old children.
For the study, researchers followed 108 mother-child pairs from birth to 2 years of age. They obtained data on the exposure to air fresheners, candles, mold, cats, dogs, carpet and environmental tobacco smoke during the prenatal, 6-month, 1-year, and 2-year timepoints. Then, they performed a skin prick test on both the mother and the 2-year-old child. A skin prick test, also called a puncture or scratch test, checks for immediate allergic reactions to as many as 40 different substances at once. This test is usually done to identify allergies to pollen, mold, pet dander, dust mites and foods. In adults, the test is usually done on the forearm, whereas children may be tested on the upper back.
The researchers found that exposure to candles during the prenatal window, cats during the 6 month window, and environmental tobacco smoke at 2 years significantly increased the risk of a positive skin prick test, thus supporting the role of the indoor environment on the development of atopic disease. They also found that combined effect of multiple exposures may be more influential to allergy development than one single exposure.
Anne Ellis, one of the study authors, said: “The increase in the average amount of time indoors means there is an increased risk of harmful health outcomes related to exposure to indoor air pollutants. Additionally, children breathe more frequently per minute than adults, and mostly breathe through their mouths. These differences could allow for air pollutants to penetrate more deeply into the lungs and at higher concentrations, making children more vulnerable to air pollutants.”
Exposure to air fresheners and candles is of particular interest, as they contain phthalates, ubiquitous pollutants with wide-ranging negative health impacts. Previous work by the same researchers had already established that indoor air freshener exposure is associated with respiratory symptoms at 2 years of age.