Updated 16 March 2018

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, although children are most vulnerable to allergies, especially allergic rhinitis.

Boys younger than 10 years of age are twice as likely as girls in this age group to have symptoms of allergies to airborne substances.

Risk factors include:

• Heredity. If one parent is allergic, a child runs a risk of 30-50% 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 60-80% likelihood of developing allergies. 

• Environment. Although heredity can determine whether you’ll have an allergy or not, it’s usually the environment that either protects you from developing the allergy, or sets the process in motion.

Some exposures promote allergies in individuals, as well as their offspring (e.g. polluted environments, exposure to cigarette smoke, and consumption of junk food and sugary drinks). On the other hand, some exposures in the environment are protective, for example fermented foods, high-fibre diets and exposure to farm animals.

• Upper respiratory tract infections. Children who contract viral or bacterial infections of the upper respiratory system (nose, throat and bronchial tubes) before they’re six months old are more likely to develop allergies or conditions such as asthma later in life. 

Although emotional stress may trigger an allergy, allergies don’t have a psychosomatic origin. 

Reviewed by Prof Mike Levin, Head of Division of Asthma and Allergy at the University of Cape Town.
MBChB; FCPaed; MMed; PhD Diploma Allergology; EAACI UEMS Allergy exam, FAAAAI, FACAAI. March 2018.


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Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies.

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