When a person is allergic to something, their immune system mistakenly believes that the substance is harmful to the body and launches an attack.

This normally causes reactions like runny or congested noses, hives or digestive issues. In extreme cases an allergic reaction can cause anaphylactic shock and even death.

Cause unknown

According to KidsHealth millions of children have some type of allergy, and in the US allergies cause about 2 million missed school days each year.

The Allergy Society of South Africa reports that up to 20% of the population suffer from allergic reactions.

Although there is much about allergies that is still not understood, an allergy usually begins with sensitisation when the person is exposed to an allergen.

Repeated exposure to this substance triggers the immune system to form the antibodies that cause the allergic reaction.

Main risk factors

There are, however, some factors that make some people more likely to become allergy sufferers.

A previous Health24 article lists three main risk factors for developing allergies:

• Genes
• Environment
• Upper respiratory infections

Genes is arguably the most important factor because it determines whether you will have an allergy or not (your susceptibility).

The environment will set the process in motion as it will determine which antigens (if any) you are exposed to. 

Upper respiratory infections are a factor because children who contract viral or bacterial infections of the upper respiratory system before the age of six months are more likely to develop allergies or conditions such as asthma later on in life. 

Parents’ role

If both parents have allergies, their children are more likely to develop an allergy, although not always the same kind of allergy.

If one parent has an allergy, a child has a 30 to 50% risk of inheriting the tendency to be allergic (atopic), although the specific allergy or allergies may different.

This means that if you’re allergic to cats and dogs, your children may be fine with pets but react violently to peanuts, eggs and kiwi fruit, for example.

If both parents suffer from allergies, their children have a 60 to 80% likelihood of developing allergies.

Further genetic connections

A study published in 2012 in the Journal of Allergy and Clinical Immunology indicates that not only are allergies inherited, but they are also gender related.

The study shows that mothers tend to pass allergies to their daughters and fathers are more likely to pass their allergies to their sons.

In both cases it was not a specific allergy that was passed on, but just the tendency toward developing allergies. 

The one exception to this tendency is an allergy to penicillin. This allergy appears not to be gender specific in any way and can be inherited from one or both parents. 

Studying allergies in twins is also a good way to determine the role of genetics in allergies, and according to ScienceABC identical twins tend to have similar allergies. The reason why they don’t always have exactly the same allergy profile is because allergic reactions are caused by genetic and environmental factors.

Because they don’t share the same genetics, fraternal (non-identical) twins are much less likely than identical twins to have the same allergies. In fraternal twins the likelihood is around 7% while in the case of identical twins it’s in the region of 65%.   

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Eugene Lotter