Review and feature article
Primary prevention of asthma and allergy

https://doi.org/10.1016/j.jaci.2005.03.043Get rights and content

The relentless increase in the prevalence of asthma and allergic diseases highlights the need for devising effective preventive strategies. Although the genetics of these disorders are being investigated, manipulation of known environmental risk factors remains the best available approach to this problem. However, the large number of potential environmental risk factors and our inability to accurately predict the development of asthma and allergy has led to conflicting data from recent prevention studies. Nonetheless, some useful recommendations can be made. Exclusive breast-feeding and avoidance of exposure to environmental tobacco smoke exposure can be safely recommended for the whole population, not only for prevention of allergy but also for other known benefits. Additionally, for children at high risk of allergy, maternal exclusion diet during lactation and protein hydrolysate as a supplement or alternative for children who could not be breast-fed seems to provide further protection. The preventive effect of avoidance of house dust mite allergen alone during pregnancy or after birth is disappointing. However, prospective randomized studies evaluating a combined food and house dust mite allergen avoidance regimen show some protection against atopic dermatitis in infancy and asthma in later childhood. Urgent research is needed to accurately identify children at high risk and to test novel preventative measures with the potential for immunomodulation. Further randomized controlled trials are also needed with long-term follow up to evaluate combined approaches that might provide maximum benefit.

Section snippets

Risk factors

During early infancy, the child is exposed to small quantities of a variety of food proteins through breast milk and larger quantities of cow's milk protein if formula fed. The normal response to the initial introduction of these proteins is immune tolerance. However, in children with atopic predisposition, this immune tolerance breaks down. Thus sensitization to foods such as cow's milk and egg is common in infancy, and in a subset of these children, clinical allergic reactions occur that

What are we trying to prevent?

Allergic manifestations are protean, and there is a lack of uniformity in definitions of outcome measures used in various studies. The definition and diagnosis of asthma and rhinitis in early childhood is most challenging in view of the lack of uniform criteria and availability of objective tests to support the diagnosis. Another complication is that early childhood allergic manifestations are often transient, and yet many studies report short-term (<5 years) follow-up periods. Most studies

Preventive strategies: Allergen avoidance, dietary manipulation, infections-endotoxin, immunotherapy, and drugs

Although there is good evidence that allergen exposure leads to sensitization21, 22 and that sensitization is an important risk factor for the development of allergic disease,23, 24 the direct relationship of allergen exposure in the causation of allergic disease is still questioned.25 The effect of exposure to allergen might depend on the nature of allergenic protein. Exposure to HDM is reported to cause asthma,26, 27 whereas dog or cat allergen exposure might be protective,28, 29, 30 although

Whole population or at-risk individuals

Because primary prevention measures require motivation, effort, and expense, most studies have targeted infants at high risk of allergy to maximize the benefit.34, 35, 36, 37 Until children can be screened for specific genes with more accurate prediction for future development of asthma and allergy, family history of allergy is often relied on to identify children at high risk. Although family history of allergy is a well-known risk factor, it remains true that the majority of asthmatic

When: Pregnancy, infancy, later childhood, or adult

The onset of allergic manifestations is usually during early childhood. Hence primary prevention efforts have to commence soon after birth or preferably during pregnancy. Animal models support the hypothesis that contact with an allergen early in life induces a state of general immune hyperresponsivenss, with increased production of specific IgE antibodies.46 Pregnancy is a TH2 environment with predominance of TH2-type cytokines. After birth, the immune system matures to achieve a balance

Preventative strategies

The identification of risk factors, such as allergen exposure, has led to evaluation of various strategies for primary prevention. The conclusive proof of effectiveness requires well-designed double-blind RCTs. However, this is not always possible. For example, the effect of breast-feeding or maternal smoking cannot be tested by means of RCTs for ethical reasons. Blinding might not be possible for practical reasons (eg, when testing the effect of exposure to pet allergens).

What we do know

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    Exposure to ETS, especially during pregnancy and early childhood, increases the risk of childhood wheeze and asthma, and avoidance of exposure to ETS must be included in all preventive advice.

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    Maternal avoidance of allergenic foods during pregnancy does not work and could be harmful.

  • •

    Breast-feeding for 4 to 6 months protects against the development of early childhood wheeze and atopic dermatitis, but there is no evidence of a long-term benefit.

  • •

    Maternal avoidance of allergenic foods during

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    Series editor: Harold S. Nelson, MD

    Disclosure of potential conflict of interest: None disclosed.

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    Copyright © 2005 American Academy of Allergy, Asthma and Immunology. Published by Mosby, Inc. All rights reserved.