allergies: nature or nuture?

From the New York Times: Researchers Put a Microscope on Food Allergies

I find research like this pretty interesting, because 4/5 members of my immediate family have celiac disese, an allergy to certain types of grain proteins, especially in wheat, rye, barley, and oats. What causes allergies? Is it genetic or triggered by environment? My dad has it, and so do me and my two sisters. Recently I found out the same gene that can cause it has also been linked to thyroid disorders, which many of my mother's sisters have, and diabetes 1, which my grandmother had. So I wonder if my sisters and I got the gene from both sides, and that's why we have it.

A lot of people have wheat sensitivities, and I think a lot more people have celiac that don't realize it. Seems like autoimmune disorders are becoming more prevalent. I wonder if they're becoming more common, or just that we're noticing more?