Why do allergy shots reduce symptoms, but not being constantly exposed to another type of allergen?

Allergies are funny like that. Allergy shots are more consistent and increase exposure gradually. Once your body has an allergic reaction it recognizes that allergen as a toxin. If you can increase a little bit at a time your body will increase it's tolerance for the allergen. In some cases, constant exposure can alleviate allergies or decrease them. In other cases allergies can become worse with exposure.One good example is poison ivy. Once you have an allergic reaction to it, the symptoms will worsen upon every exposure. Your body is constantly changing as well. Some of us outgrow allergies and sometimes new ones develoip.