Parent's Resource Center

Understanding How Allergies and Asthma Develop

If asthma or allergies run in your family, you probably already know that your child is at risk for developing allergic disease, too. Like many parents, you may find yourself digging into the mountain of research on predicting and preventing allergies and asthma. It doesn't take long to find conflicting opinions. Sometimes just understanding what is being studied (and why) is baffling. All of this can be frustrating for parents who only want to protect their child.

A basic understanding of how allergic disease develops may help you grasp the medical research on predicting and preventing allergies and asthma. Keep in mind that the medical community's perception of allergic disease changes as new research is published. That's one reason for differing opinions, even among medical doctors.

The hallmark study

The natural history of allergic disease was documented by a long-term study published in 1995. The study was conducted jointly by the Kaiser Permanente Medical Center Department of Allergy and the University of California Department of Pediatrics, both in San Diego, CA. High risk infants (those with a family history of allergic disease) were followed from birth to age seven. They were tested for atopy (allergic disease) at age 2, age 4, and age 7.

The Kaiser study identified the path of pediatric asthma development in high risk children. It looks like this:

  1. Atopic dermatitis: Skin allergy symptoms (eczema -- patches of dry, red, flaky skin) appeared first, often in infancy.
  2. Food sensitivity: In early infancy, the children who later developed allergic disease were already sensitized to egg, cow's milk, and peanuts. Food sensitivity was detected by evidence of immune system activity in blood tests.
  3. Food allergy: Children who showed true food allergy by age 4 had a higher incidence of allergic rhinitis (hay fever) and asthma at age 7.
  4. Respiratory symptoms:  Most of the children who developed respiratory symptoms by age 7 had already displayed the symptoms of eczema (first), food sensitization (second), and food allergy (third).


Some of the children in the study dropped off the asthma development path at every stage. That is, not all the infants who first had eczema developed food sensitivity later, and so on. That tells researchers (and parents) that something else is contributing to the development of allergic disease. All of the children in the study were genetically pre-disposed to allergic disease. Why did some children develop each of the predictors and finally respiratory symptoms, while some did not?

Exposure to allergens leads to allergies

The 1995 Kaiser study suggested that environmental factors may have tipped the scales. This led to more research. Study after study validated the relationship between sensitization (prolonged exposure to allergens) and the development of asthma. Today, the American Academy of Allergy, Asthma & Immunology (AAAAI is the most respected asthma authority in the U.S.) confirms that early and prolonged exposure to allergens contributes to the later development of asthma and allergies.

Prevention may be possible

That means it may be possible to prevent allergic disease by avoiding early exposure to allergens and irritants, particularly viruses, dust mites, animal dander, cockroaches, mold and mildew, and smoke. Avoiding exposure to these allergic triggers early in childhood usually means scrupulous environmental-control measures.

Trigger avoidance techniques might include keeping infants and toddlers away from tobacco smoke and people who have viral infections and removing pets from the home. Clinical trials demonstrate that encasing bedding in dust mite-proof covers and aggressive household cleaning are two of the most effective ways to avoid sensitization and slow down the development of allergic disease.

The more you learn about avoiding asthma triggers now -- even before allergic symptoms appear -- the better your chance of protecting your child from allergies and asthma later.

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Revised: November 14, 2006