What is an allergy?
An allergy or hypersensitivity is one of the most common ailments that arises due to abnormal functioning of the immune system. It is a result of exposure to a specific antigen (allergen) by a sensitized person who has already developed antibodies against the allergen in question.
The interaction of the allergen with the antibody can result in an allergic reaction in many of these sensitized individuals. However, not ever person harboring specific antibodies to certain allergens develops an allergic reaction – some are only sensitized but it does not progress to an allergic reaction.
What are the types of allergic reactions?
There are four types of allergic (hypersensitivity) reactions based on the mechanism of the reaction. The types I, II, and III allergic reactions are antibody mediated reactions, while type IV is a T-cell mediated reaction.