In doing some research I was intrigued by a study involving children which found a correlation between the intestinal parasite Giardia Lamblia and food allergies, and the authors theorized that it was because of the parasite causing "antigen penetration through damaged intestinal mucosa". It's a particularly interesting study because they found that total IgE (Immunoglobulin E, which represents antibodies produced against allergens) and IgE antibodies to specific foods were significantly higher in the Giardia group. Further, they found that other parasites did not cause the same IgE elevation, so it appears Giardia is unique in that regard. To view this interesting study, click here.
Another study found a potential correlation between Giardia and Urticaria (Hives) and Pruritis (skin itching). Upon treatment of the parasite, the skin symptoms disappeared. Check out the study here.
How common is Giardia? It is the most common intestinal parasite in the United States according to the CDC. Giardia is transmitted from both food and water.