What causes you to develop an allergy in the first place?

Is it your genetic makeup? Something in our food supply? Something you ate too much of as a kid? A great deal of research has been devoted to answering these questions, and the best answer that researchers have developed so far is that food allergies are caused by a combination of nature (your genes) and nurture (what you eat). The best evidence available for a genetic connection comes from studies of peanut allergy in twins. The medical community knows that allergies run in families, so the genetic link is well established, but we also know that children in the same families —even twins — do not always share the same allergies. This has led researchers to suspect that genes account only for a susceptibility to food allergies. If parents have hay fever or asthma, for example, their children are more prone to developing an allergic disease, including hay fever, asthma, eczema, or food allergy. One child may develop food allergy, another may develop hay fever, and a third may be allergy-free. Why this happens is still largely a mystery.