What is Hypersensitivity?

a doctor doing a hypersensitivity check on a patient's hand


The immune system is necessary for protecting your body from damage caused by any harmful invasive substance that is capable of causing infection in the body.

But sometimes your immune system mistakenly considers a harmless substance as a harmful substance that will harm your body. This mistaken behaviour is called a hypersensitivity response.

So a foreign substance that can be toxic which causes this immune reaction to occur is called an allergen or antigen. So when your body detects some potential threat in response to it, your immune system builds a barrier to shield it from such foreign substances.

Depending upon the antigen to which the person gets exposed your body is capable of producing different types of hypersensitivity reactions. 

So let's have a look at different types of hypersensitivity reactions we have known till now.

What Is A Hypersensitivity Reaction?

An unnecessary reaction that your body provides to an antigen is called a hypersensitivity reaction.

There are 4 different types of hypersensitivity reactions. Some studies also suggest a potential 5th type.

Every reaction differs from the other reaction in the way the body differentiates the type of antigen, how fast the body reacts to this foreign substance, and what is the way your body reacts to it.

There are many instances in which people called it by the name of allergies.

Difference Between Hypersensitivity And Allergy

For quite a long time many people have used such terms interchangeably. Allergic reaction is the condition in which people experience symptoms and signs of such reactions while hypersensitivity reaction is the process in which the immune system reacts to a sensitive foreign body.

Type 1 Hypersensitivity Reaction

When a person has exposure to an antigen then the body responds immediately so this type 1 hypersensitivity reaction occurs. In this method, the body responds to a foreign harmful substance or antigen with a particular type of antibody called IgE.

What Can Trigger Type 1 Hypersensitivity?

  • Food products such as soy nuts and shellfish.
  • Animal sources can be rats, cats, or bee stings
  • Some environmental sources, such as latex, mold, and dust
  • Certain allergic conditions, such as asthma, conjunctivitis, and allergic rhinitis.

Stages Of Type 1 Hypersensitivity 

  1. Sensitization stage and
  2. The effect stage.

When the person encounters some kind of antigen but does not go through any symptoms then this is called the sensitization stage. While in the effect stage, when again the person encounters the antigen and this time when the body recognizes the same antigen it produces some of the response which is characterized by some symptoms which are similar as in the case of allergy.

Physical symptoms of type 1 hypersensitivity are

  • Flushing
  • Rash
  • Hives
  • Itching
  • Wheezing
  • Edema
  • Rhinitis
  • Stomach aches

Some Other responses are

  • Nausea and vomiting
  • Breath shortness
  • Severe cardiac symptoms
  • Loss of consciousness


Firstly the doctor will examine the symptoms and will look at his medical history.

There can also be some allergy or any kind of related blood test which helps the doctor to identify the antigen. Treatment may vary from immediate medical treatment and on the other hand some prescribed medication to the people with mild symptoms. Additionally, people should try to avoid such allergens in the future.

Type 2 Hypersensitivity Reaction

Similar to type 1, the type 2 hypersensitivity reaction also has antibodies. They both belong to the same category of antibodies known as IgG. All that constitutes a difference in the form of antigen. Also, type 2 hypersensitivity involves IgM antibodies.

In type 2 hypersensitivity there are cytotoxic reactions in which a healthy cell dies in making a response to the antigens which can cause long-term tissue and cell damage. Such damage involves the further reaction

  • Immune thrombocytopenia, a blood disorder if your body lacks platelets
  • When the body destroys neutrophils results in  autoimmune neutropenia
  • On bursting of RBC, exist autoimmune hemolytic anemia
  • Graves disease

Drugs For Type 2 Hypersensitivity 

  • Thiazides
  • Penicillin
  • Methyldopa
  • Cephalosporins


  • Systemic glucocorticoids
  • Cyclophosphamide and
  • Cyclosporin agents
  • Plasmapheresis
  • Intravenous immunoglobulin

Type 3 Hypersensitivity Reaction

In type 3 hypersensitivity many antibodies and antigens formed the complexes in the joints, blood vessels, skin, and many kidney issues. Such complexes can cause a chain of reactions that further leads to damage to the tissue.

Some Causes Of A Type 3 Hypersensitivity reaction

  • Certain drugs have proteins from various organisms.
  • Other drugs like infliximab to manage autoimmune conditions
  • Animal sources like insect stings.

Type 3 Hypersensitivity Reactions Can Also Lead To:

  • Lupus
  • Serum sickness
  • Rheumatoid arthritis
  • Small-vessel vasculitis
  • Henoch-Schönlein purpura


There is various treatment options present there which depend on the presentation and severity of the hypersensitivity response. So the basic treatment is to involve the control of the underlying condition.

Type 4 Hypersensitivity Reaction

These are the cell-mediated type 4 hypersensitivity reactions. The white blood cells called T cells control type 4 hypersensitivity reactions instead of antibodies. These reactions can be subdivided into type 4a, type 4b, type 4c, and type 4d which are based on the type of T cell involved.

Type 4 hypersensitivity differs from the other three in the situation that it can result in a delayed reaction.

Subsets of Type 4 Hypersensitivity 

  • Contact dermatitis
  • Granulomatous-type hypersensitivity
  • Tuberculin-type hypersensitivity

The basic cause for type 4 hypersensitivity reactions are your exposure to certain specific metals, poison ivy, and other drugs such as some antibiotics.

Type 5 Hypersensitivity Reaction

When an antibody targets some receptors which lie on the cell surface. So a response to such action is type 5 hypersensitivity.

Some studies even show that this is typically a subset of type 2 rather than being unique.

Take Away

The treatment and diagnosis may vary according to how a person experiences the type of hypersensitivity reaction and with further conditions and symptoms that will result from the reaction.  So one should be considering the basic cause that is leading you towards the hypersensitivity reaction to getting away from further loss.