Updated 31 May 2017

Heredity as a risk factor in allergic reactions

Three factors increase a person’s chances to have an allergic reaction. These are heredity, the immediate environment and upper respiratory infections.


Three factors increase a person’s chances to have an allergic reaction. These are heredity, the immediate environment and upper respiratory infections.

If one parent is allergic to a particular substance, a child runs a risk of 30-50 percent of inheriting the tendency to be allergic, although, interestingly enough, he or she may not necessarily contract the parent’s particular type of allergy. They inherit a general tendency to develop allergies.

Early exposure to possible allergens, such as cat fur or cigarette smoke is also believed to increase the tendency to develop allergies.

If both parents have allergies, their children have a 60 –80 percent likelihood of developing allergies Only 25-50 percent of identical twins share the same type of allergy. If neither parent has allergic tendencies, a child’s chances of developing them drop to about 10 percent.

Even though heredity determines whether you will have an allergy of some sort, it is usually the environment that sets the process in motion. If you have inherited an allergy to a specific type of pollen, you might not even know this until you move to an area where this pollen is prevalent.

An allergy is an abnormal sensitivity or reaction of your immune system to a substance (an allergen) that you inhale, eat or touch. This substance usually has no effect on non-allergic people.

It is difficult to determine what exactly determines a particular person’s allergic reaction to certain substances. An allergy usually begins with a sensitisation when the person is initially exposed to an allergen. The repeated exposure to an allergen - this could last from several days to a few decades – triggers the immune system to form antibodies that cause the allergic reaction to the specific antigen.

Allergies occur across the age, sex and race spectrum. It can start at any age, although children are most vulnerable to allergies.

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

It is important to keep in mind that the severity of an allergy can increase significantly over time. A first bee sting could cause a mild allergic reaction in an allergic person, whereas, a sixth or seventh could be fatal.

This is also the reason that initial mild reactions should be taken seriously and not merely seen as a temporary inconvenience.

Read more:
How mast cells work

Allergy Society of South Africa (ALLSA)


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.

Ask the Expert

Allergy expert

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.

Still have a question?

Get free advice from our panel of experts

The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.

* You must accept our condition

Forum Rules