Is There an Allergy Epidemic?

Has there been a rise in allergies?

Allergic rhinitis (hay fever), asthma and atopic eczema are among the most common causes of chronic ill health. There is also clear evidence that in the Western world these disorders are increasing in frequency. In Sweden, for example, the number of children with allergic rhinitis, asthma or eczema has doubled over a 12-year period.

What causes allergies?

The development of allergic disease relates to a complex interplay of genetic and environmental factors. Since minimal genetic changes occur over a short period of time, such as the last two decades, we must assume that environmental factors are most likely responsible for this trend. The reunification of Germany offered tremendous insight into the impact of environmental changes on allergic conditions. These disorders were less common in East Germany than in West Germany before reunification, where as since that geopolitical change occurred, the prevalence of allergic problems (except asthma) has increased among children who spent their early childhood in East Germany.

What is the 'Hygiene Theory' of allergy formation?

This interesting observation raises the possibility that somehow the Western lifestyle accounts for this change. Perhaps this Western lifestyle deprives the developing immune system sufficient exposure to infectious agents, to nurture "allergy protective" infection-fighting immune responses. A relatively clean environment and the use of antibiotics for minor illnesses in early life may sway the immune system towards "allergy promoting" responses instead.

This describes the so-called "Hygiene Theory", which attempts to explain the rising incidence of allergic diseases. Other examples, which illustrate this, include:

  • Lower incidence of allergy in those living on farms (or rural areas) due to more exposure to bacteria in barns.
  • Lower incidence of allergy in younger children of large families (three or more older siblings) due to repeated exposure to infection from older siblings.
  • Lower incidence of asthma and wheezing in children who go to day care centers, where they are exposed to more infections.

The Hygiene theory however, cannot explain the higher rates of allergic asthma among poor African Americans in the inner city areas. It is possible that other cofactors are required for the development of asthma, such as respiratory viral infections, exposure to allergens (such as dust mite and cockroach), tobacco smoke and air pollution (including diesel fumes). It is an exciting time for all of us involved in caring for people with allergies and asthma. Within the next 10 to 20 years, we are likely to gain a greater understanding of the immune events that result in these common and fascinating disorders. This insight will bring us ever closer to a cure.


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Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care


"Allergic rhinitis: Clinical manifestations, epidemiology, and diagnosis"

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