Allergies are one of those things that scientists and doctors still have quite a bit left that we don't understand. For some reason, there are some people who seem to have a predisposition to developing allergies to certain things in the environment. For most children, that risk is somewhere around 20%. If one parent is allergic, the child will be allergic about 1 out of 3 times. If both parents have allergies, then there is more than a 50% chance that the child will also have allergies. This information shows us that there is a strong genetic component to allergies.
There is also some evidence that the cleanliness of modern society plays some role in the increased rate of allergies as well, in that our bodies don't have such a broad exposure to other allergens and germs, and so that decreased exposure makes it harder for our immune system to "learn" what is ok to react to and what it should not react to. Inappropriate immune responses to things that do not merit a response is one way to explain what allergies are. Unfortunately, the answer as to why some people have them and others don't is still a mystery. Please contact your doctor
if you have questions or concerns.