Unfortunately, the system can go wrong and lead to conditions that result in tissue damage and death. There are two broad classes of hypersensitivity reactions which can be broken up into four types.
All allergenic antigens are polyvalent, so they bind other IgE, cross-linking receptor complexes.
Skin grids are useful for detecting if a person will respond to an allergen. Risk of sensitizing the individual as well as leading to shock. Chicken egg albumin, casein, almond, scallops, etc. Kentucky blue, red top, perennial rye, Bermuda, fescue, etc. Aspergillus, Rhizopus, etc.