What Causes Allergies?

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What Causes Allergies?

One of the first questions my patients ask me when I diagnose them or their children with allergies is, “Why me?” The answer is not always clear, but likely has many factors. First, allergies tend to run in families, so if one or both of a person’s parents have allergies, it is extremely possible that they will have allergies as well. This inherited tendency for allergies is caused by any number of genetic mutations that makes the immune system react abnormally to harmless substances.

The environment also likely plays a role in the development of allergies. Exposures to different substances, both to the fetus and the infant, can have an effect on the development of allergies. For example, early introduction to highly allergenic foods in young children may predispose to food allergies and atopic dermatitis. Pet exposure may also influence the development of allergies, with various studies suggesting that multiple pets in the home during early childhood can be protective against the development of allergies. Infections also play a role in the development of allergies – for example, infection with the respiratory syncytial virus during infancy appears to be a risk factor for the development of asthma.

Ultimately, the cause of allergies is probably not a single event, but multiple events occurring together. These likely include certain environmental triggers occurring in a person with genetic susceptibilities to allergies.

Concerned that you are predisposed to allergies? Then learn about the prevention of allergies and asthma.


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Mandhane PJ, Sears MR, Poulton R, et al. Cats and Dogs and the Risk of Atopy in Childhood and Adulthood. J Allergy Clin Immunol. 2009;124:745-50.

Salo PM, Zeldin DC. Does Exposure to Cats and Dogs Decrease the Risk of Allergic Sensitization and Disease? J Allergy Clin Immunol. 2009;124:751-2.

Fiocchi A, Assa’ad A, Bahna S. Food Allergy and the Introduction of Solid Foods to Infants: A Consensus Statement. Ann Allergy Asthma Immunol. 2006; 97: 10-21. 

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