Contrary to what most people think, allergies are not the inability of the body to handle a particular stimulus. Rather, it is the hypersensitivity to a stimulus that causes the body to react in its effort to expunge the irritant. It is classified as a disorder afflicting the immune system. Note, it is a disorder, not a deficit. In the case of cheesecake allergies, it is the hypersensitivity to chemicals and substances in the cheese.