The exact cause of allergies is unknown, but researchers suspect that they are most likely caused by a combination of both genetics and environmental factors.
Studies show that if one parent is “atopic”, at least 30% of their children will have allergies[i]. If both parents are atopic, this value goes up to 50%. Although a familial history of allergy puts you at an increased risk of developing allergy, you will not necessarily develop the same type of allergy or allergic disease as your family member[ii]. Atopy describes a predisposition for allergic disease in general. The presentation and type of allergic disease may vary from family member to family member (for example, a parent has an allergy to pet dander and their child has an allergy to milk protein).
Not all individuals with a genetic predisposition for allergies will go on to develop them because the environment plays an important role too. It is difficult to know how much is determined by genetics and how much is determined by environmental factors because family members are often exposed to the same environmental factors. Research on identical twins raised in different environments has shown that there is some discrepancy in the development of allergies despite a shared genetic predisposition. This suggests that although there is a strong genetic component, environmental exposure is quite influential as well[iii].
What can you do?
You cannot modify a genetic predisposition for developing allergies (at least not yet!), you can alter the environmental exposures, which influence the development of allergies. External environmental factors like smog, car exhaust, pollen, etc are difficult to alter unless you move to a different location. However, it is possible to reduce the indoor environmental factors in your home. Whether or not this is effective in preventing allergies in those predisposed to them is still unclear but it certainly couldn’t hurt. There is also a great deal of interest in whether dietary modifications, both for the mother during pregnancy and for the infants during the first year or life, can protect infants predisposed to developing allergic disease. At this point, there is not enough evidence to make a strong recommendation on preventive practices. However, research shows that introducing foods (anything other than breast milk or formula) during the first 4 months of life is associated with the development of allergies so refraining from this is one more way you may be able to protect your little one from developing allergies.
[iii]Los H, Postmus PE, Boomsma DI. Asthma genetics and intermediate phenotypes: a review from twin studies. Twin Res. 2001;4:81-93.
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