Hypersensitive Reactions (Allergic Reactions)
Allergic reactions occur when the immune system responds abnormally to common substances such as pollen, dust and certain foods.
For those who are allergic, they can cause reactions upon skin contact or when they are breathed, swallowed or injected.
Allergic reactions are quite common and may happen seconds to hours after contact with the allergen.
Some reactions may take more than 24 hours to appear.
Though many allergic reactions are mild, others may be dangerous or life-threatening.
They may be localized, involving a small part of the body or may affect a large area or the whole body.
Certain metal jewellery or certain cosmetics may cause skin rash in some, for example.
In response to this trigger, the body starts making a type of protein called IgE or immunoglobulin E.
IgE molecules bind with the allergen molecules in an antigen-antibody reaction.
This attachment of the antigen and antibody leads to the release of some chemicals (such as histamine) in the body.
These chemicals cause the inflammatory symptoms of allergic reactions such as rashes, itching and sneezing.
Two British immunologists, Coombs and Gell, have classified allergic reactions into four types, Type I, II, III and IV.
Type I, II and III allergic reactions are called immediate types of allergic reactions because they occur within twenty-four hours of exposure to the allergen. Type IV reactions typically occur after 24 hours of exposure and are called delayed allergic reactions.
02. Type II - Cytotoxic Reactions
03. Type III - Immunocomplex Reactions
04. Type IV - Cell-Mediated Reactionns