Types of allergy are classified to denote cause, severity and possible management and prevention.
• Type I hypersensitivity
This is also known as immediate or anaphylactic-type reactions. This may be caused due to pollen, foods and drugs and insect stings.
• Type II hypersensitivity
This involves specific antibodies called the Immunoglobulin G (IgG) and IgM. There is binding to and destroying the cell the antibody is bound on.
This type of reaction is seen after an organ transplant when the body refuses to see the transplanted organ as its own.
• Type III hypersensitivity
This is an Immune complex-mediated reaction. The immune complex is the bound form of an antibody and an antigen.
This leads to a cascade of reactions in the body which goes on to destroy local tissues. Examples of this condition include glomerulonephritis and systemic lupus erythematous (lupus, SLE).
• Type IV hypersensitivity
Delayed or cell-mediated reactions are mediated by special immune cells called the T-cell lymphocytes.
The T cells take from a few hours to a few days to mount an allergic response. Examples include contact dermatitises such as poison ivy rashes.
Allergies commonly signify Type I hypersensitivity. This includes allergic rhinitis characterized by runny nose, and eyes and sneezing.
Two major categories are seasonal allergic rhinitis (SAR) and perennial allergic rhinitis (PAR). While SAR is associated with exposure to pollen at certain seasons PAR occurs almost all around the year.
Allergic rhinitis affects an estimated 20-40 million people in the United States.
Other varieties of type 1 reaction are food and drug allergy and allergies due to insect venom.
Insects that may lead to allergies include bees, wasps, yellow jackets, ants, hornets etc.
Allergic asthma is also a type 1 allergic reaction. This occurs when the allergen is inhaled.
Common allergens include pollen, animal dander, fungal spores or moulds, dust mites etc. There is severe wheezing, shortness of breath, cough and thick mucus secretions.