Allergies as We Age
It is true, unfortunately, that people can develop allergies at any age. It all depends on exposure and your genes. Let's say your genes have decided ragweed is harmful. Upon your first exposure to ragweed (which might not be until you're 30), your body creates very special versions of the antibody Immunoglobulin E (IgE). These are custom designed for the allergen it has decided is a threat. Once this IgE has been created, it binds to mast cells, now primed for the next exposure. Upon re-exposure, the IgE of the mast cells binds to the allergen and the allergic response, helped along by histamine, begins.
This is the why people need to be wary of bee stings even if they've been stung before. "The fact that you managed to survive the first reaction does not by any stretch of the imagination mean that the next will not be bad," says White.