About 15% of children have seasonal allergies by their seventh birthdays, according to a study in the November 2000 issue of the Journal of Allergy and Clinical Immunology. Boys, firstborn children, those with eczema, those with food allergies, and those whose parents have seasonal allergies are all more likely to develop seasonal allergies. Early wheezing does not appear to increase the chances.
It takes more than one exposure before an allergy can develop, thus food allergies often appear at a younger age than seasonal ones. There is a marked increase in seasonal allergies after the second year of life, suggesting that for most children at least 2 seasons of pollen exposure are needed before seasonal allergies are noticeable.
Children born in spring or early summer have their allergies show up earlier than those born at other times. Parents are often told that their children are too young to have allergies. While allergies do become more common from ages 2 to 7, they certainly can be present earlier.