5) An allergy is when your immune system is triggered by and hypersensitive to a substance that doesn't normally bother most people. Take me through the steps of sensitization to an allergen upon a first encounter/response. Then walk me through the steps of a second encounter with the allergen. Finally, discuss why some substances may be more hyper allergenic, while others are hypoallergenic, In other words, what makes them more prone to being seen by an immune system as foreign and problematic..