Allergic reactions are exaggerated sensitivities that come about when you come into contact with an allergen, and your immune system responds abnormally to it. The reactions are often common and happen seconds to hours after contact with the allergen.

Although most of the reactions are mild, some are dangerous or life-threatening, so it’s recommended you see an allergy doctor whenever you have an allergic reaction, regardless of its nature.

What are the 4 types of allergic reactions?

The classification of the allergic reactions was done by two British immunologists: Gell and Coombs. And they categorized allergic reactions as type I, II, III, and IV.

The first three categories are known as immediate types as they occur within 24 hours of exposure to the allergen. Type IV occurs after 24 hours; hence the name delayed allergic reactions.

Would you love to know more about the reactions? Here they are:

Type I or Anaphylactic reactions.

These reactions result from an antigen cross-linking with membrane-bound IgE antibodies of Basophil or mast cell. Serotonin, bradykinin, histamine, and lipid mediators such as prostaglandins and leukotrienes are released during the reaction.

These released substances often have the potential to cause tissue damage.

Most common types of type 1 allergic reactions include: allergic dermatitis, bronchial asthma, allergic conjunctivitis, allergic rhinitis, allergic shock, and allergic dermatitis.

Allergic shock is the most severe form of a medical emergency as it can lead to a life-threatening respiratory failure. People suffering from the condition often have extreme breathing problems, low blood pressure, swelling, shock, and bluish skin.

Type II or Cytotoxic reaction

These types of allergic reactions are mediated by IgM and IgG antibodies. In these reactions, the antibody reacts directly with the antigen bound to the cell membrane hence inducing cell lysis through complement activation.

The most common types of cytotoxic reactions are blood transfusion reactions, Rh incompatibility of a newborn, and autoimmune diseases such as autoimmune hemolytic anemia, Pemphigus Vulgaris, Goodpasture’s syndrome, and Bullous Pemphigoid.

Type III or immunocomplex reactions

These are also mediated by proteins, i.e., IgG and IgM antibodies. These antibodies react with the allergen to form immunocomplexes (antigen-antibody complexes) responsible for the reaction.

The active complement results in activatin and PMN chemotaxis. PMNs then release tissue-damaging enzymes.

Type III reactions are common in Arthus, serum sickness, and lupus reactions.

Type IV or cell-mediated reactions

As mentioned above, these reactions are also known as the delayed type of hypersensitivity, and they happen at least 24 hours after exposure to the allergen. In most cases, the reactions take 48-72 hours or longer to appear after you have come into contact with the allergen.

The reactions are initiated by T-lymphocytes and mediated by macrophages and T-cells. The response involves the interaction of antigens with the surface lymphocytes.

According to experts, most long term infectious diseases such as fungal infections and tuberculosis belong in this category. Certain skin sensitivity reactions, especially those involving metals, also belong here.

Hypersensitivity key takeaways

To drive the message home, here are 5 things you should take away from the various types of allergic reactions:

• Type I and III are mediated by antibodies, while T cell lymphocytes mediate type IV.
• Type I hypersensitivities involve IgE antibodies that initially sensitize someone to an allergen and provoke a quick inflammatory response upon further exposure. The most common types under this category are allergies and hay fever.
• Type II hypersensitivities involve binding IgG and IgM antibodies to antigens on cell surfaces. This triggers a series of events that lead to cell death. Common types of reactions under this category are hymolytic diseases and hemolytic transfusion reactions.
• Type II reactions are a result of the formation of antigen-antibody complexes that settle on tissues and organs. In an attempt to remove these complexes, the underlying tissue is also damaged. The most common examples under these categories are rheumatoid arthritis and serum sickness.
• Type IV hypersensitivities are regulated by T cells and are delayed reactions to antigens associated with cells. Chronic asthma, tuberculin reactions, and contact dermatitis are the most common types under this category.

You should note that any type of hypersensitivity has the potential to turn lethal, so visit an allergy clinic Manassas VA and have the condition diagnosed and treated.