ALLERGIES ON THE INCREASE
The incidence of allergies and related conditions such as asthma and food allergies is
increasing around the world. It is estimated that up to 1 in 3 people are allergic to one
or more substances (allergens) at some point in their lives.
Hayfever, which was first recognized in England over a century ago, used to be an
uncommon disorder, affecting less than 10% of the population. Allergic rhinitis, which is
the medical name for hayfever, now occurs in at least 25% of the population.
Significant increases have also been noted in the incidence of bronchial asthma and of
food allergies, such as peanut allergy.
No one knows for sure why allergies are on the increase, but there are two leading
The "hygiene hypothesis" suggests that a lack of childhood infections skews
the immune system so that it is more likely to recognize common substances such as pollens
as dangerous. Vaccinations, antibiotics, and improved sanitation have all changed the
environment in which a childs immune system develops.
Children living in more developed countries, in urban areas, with fewer siblings, who
do not attend day care, and who are not around farm animals or cats are all more likely to
develop allergies and asthma.
The other theory suggests that air pollution, especially diesel exhaust particles,
plays a role. For example, the prevalence of allergies seems to parallel industrialization
in many countries. There is research that diesel exhaust particles and other pollutants
can act directly to affect the immune system. In either case, it is important to recognize
and treat allergic diseases early before serious reactions, tissue damage, or chronic