What if you have an allergic reaction to an environmental allergen you’ve been exposed to your entire life, but it does not show up on your IgE allergy test? Your body may have become desensitized to that reaction over time, with continuous exposure, or you may not actually be allergic to that particular environmental allergen.
Tolerance is your body getting used to the allergen overtime, to where your immune system recognizes the allergen and it doesn’t have the same strong reaction as before. For example, if you're allergic to cats and you’re exposed to a new cat, you might find that over time your cat dander allergies get better. But if you go away from home for a while, and come home to the same cat, you might sneeze again. That’s because your body has lost tolerance to the allergen with time away from the allergen. Something similar is being done with food with oral immunotherapy (OIT)!
IgE testing for environmental allergies is the opposite of IgE food testing, as it has a high positive predictive value on average. This means there are far less false positive results. If you have a positive result to an animal dander, insect, tree or grass allergen, chances are that is a true IgE allergy.