<unk>  (or immediate hypersensitivity) is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type I is distinct from type II, type III and type IV hypersensitivities. Exposure may be by ingestion, inhalation, injection, or direct contact.
Type I hypersensitivity
Type II hypersensitivity
Type III hypersensitivity
Type IV hypersensitivity
Histamine intolerance
Hypersensitivity
Pseudoallergy
Allergy