Why are some people not allergic to anything at all?

No one knows...: I hear ya. Allergies are common and increasing in frequency, but in truth still only occur in a minority of people. A very loud minority, given the complaints of pollen allergy in the spring. But it's not just environmental allergies; the prevalence of other allergic conditions are on the rise, too - notably food allergy. On the flip side, only those with strong immune systems get allergies!