Epidemiology of allergic disorders – risk factors and the allergic march

Author(s):
Gary W.K. Wong MD, FRCPC

Over the years, we have seen the rise of allergies. More people have been affected by this and is now dubbed as the most common chronic disorders affecting adults and children alike.

Among the risk factors of allergies is exposure to the allergen. But one of the most prevalent concepts in allergy development remains to be the hygiene theory, wherein it was made evident that exposure to allergens may not be as harmful as we think but may help with the tolerance of our immune response and later lessens risk of allergy development.

Key messages:

• In developed countries, one in three children suffers from at least one allergic disorder.

• Although exposure to allergens has been considered to be an important factor in the past, it is now clear that early exposure may not be harmful.

• Living on a farm and exposure to farm animals is associated with protection against allergies. Such protection has been linked to the exposure to environmental microbes which may have the potential to modulate the early immune system so as to prevent the subsequent development of allergic disorders.


Allergic disorders have become the most common chronic disorders affecting both children and adults. In developed countries, one in three children suffers from at least one allergic disorder.1 Food allergy and infantile eczema are frequently the first manifestations of a life-long problem of allergies. Allergic rhinitis and asthma usually manifest at 3 to 5 years of age.

Such sequence of manifestations of allergic disorders has been described as the allergic march. Over the past 3 decades, major advances have been made in terms of the treatment of established allergic disorders. These advances include the development of different preparations of steroid delivered typically onto the skin or locally into the nostrils or the lower airways so as to minimize the systemic side effects.

Many preparations of biologics are now available for severe and refractory asthma or atopic dermatitis. Recent attention has shifted to the development of potential primary preventive treatments, such as the use of infant formula which may facilitate protection against allergic diseases.2

However, the exact causes of these allergic disorders remain unclear. It is now widely accepted that the manifestations are due to complex interactions of genetic and environmental factors (Figure 1). Although exposure to allergens has been considered to be an important factor in the past, it is now clear that early exposure may not be harmful. In the case of peanut allergy, evidence revealed that early exposure was found to be beneficial in preventing subsequent manifestations of peanut allergy in high risk infants.3