Updated 01 June 2017

Risk factors for allergies

Risk factors for allergies are heredity, environment and upper respiratory infections.


Allergies occur across the age, sex and race spectrum. An allergy can start at any age. Children are most vulnerable to allergies, especially allergic rhinitis. Boys younger than 10 years are twice as likely as girls in this age group to have symptoms of allergies to airborne substances.

Risk factors

  • Heredity – if one parent is allergic, a child runs a risk of 30 to 50% of inheriting the tendency to be allergic, although he or she may not necessarily develop the parent’s particular type of allergy. If both parents have allergies, their children have a 60 to 80% likelihood of developing allergies. Only 25 to 50% of identical twins share the same type of allergy.
  • Environment – although heredity determines whether you will have an allergy of some sort, it is usually the environment that sets the process in motion. The environmental factor has an influence when you are in a place where you are exposed to high levels of a specific antigen, especially early in life. 
  • Upper respiratory infections – children who contract viral or bacterial infections of the upper respiratory system (nose, throat and bronchial tubes) before they are six months old are more likely to develop allergies or conditions such as asthma later on in life. 
    Although emotional stress may trigger an allergy, allergies do not have a psychosomatic origin. 

Read more: 

Preventing allergic reactions

Treating allergies  

Causes of allergies

Revised and reviewed by Professor Sharon Kling, Allergologist, Clinical Head of the Paediatric Allergy Clinic at Tygerberg Hospital and Associate Professor of Paediatrics, University of Stellenbosch. March 2015.


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