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Allergic disorders are thought to have become more common in North America and Europe during the last 15 to 20 years, and researchers are trying to determine the reasons. In particular, the incidence of the “allergic triad” — rhinitis, asthma and nasal polyps — has almost doubled in many countries since the 1970s. 
One survey of allergies among Welsh children found that between 1973 and 1988 the number with hay fever rose from 9 to 15 percent. And the number of children suffering with asthma increased from 6 to 12 percent and the number suffering from eczema rose from 5 to 16 percent.
Other studies record a doubling of the numbers of U.S. children admitted to hospital with asthma since the 1970s.
[box style=”rounded”]Not only hospitalizations but also deaths from asthma have been increasing. In the U.S., for example, more than 5,000 asthma deaths were reported in 199[/box]
The number of fatalities more than twice that for 1977 — with no clear reason. Death rates from this condition have also risen in Europe, Australia and other developed nations.
The “allergic march”
Although allergy can strike at any age, a first allergic episode frequently appears before the age of five, and the condition may disappear with increasing age. For example, atopic dermatitis (eczema) almost always makes its first appearance in infancy or early childhood, and resolves as the child gets older. Cow’s-milk protein allergy, also common in infancy, tends to vanish as the baby’s immune system matures. While some allergies, particularly food allergies, often persist into the teen and adult years, few of the elderly still sneeze their way through the hay-fever season.
Sometimes allergies change as children mature, with one group of symptoms being replaced by another in a characteristic pattern called the “allergic march.” Early food sensitivities may be replaced by sensitivity to airborne allergens (aeroallergens), causing nasal and lung problems.
For example, as an infant Jenny suffered from eczema all over her face. The eczema disappeared by the time she was about a year and a half, only to be replaced by hives and vomiting immediately after she ate eggs. These symptoms resolved a couple of years later, but Jenny went on to develop hay fever in her teens. Her hay fever may well lessen in later life, so she will have fewer symptoms.
Epidemiologists, who study the distribution and causes of diseases, believe that some of the reported surge in allergic disease is only apparent, reflecting greater public and media interest. Allergy awareness is a fairly recent phenomenon and, together with the greater likelihood of accurate diagnosis, may partly explain the apparent rise.
As one woman, now a senior, puts it: “When I was a child I used to get attacks of a sniffly thing, with sneezes and coldlike symptoms. I would just go to bed for a few days.
Today I would probably be diagnosed as allergic, but then we wouldn’t have thought of allergy or even gone to a doctor. We knew about hay fever and asthma, and we’d heard some horror stories of people dying from insect bites, but that was about it; we just wouldn’t think of allergy as an explanation