Hypersensitivity- Definition, Causes, Mechanism, Types, Examples


Hypersensitivity is a term that describes an abnormal or excessive immune response to a foreign substance, also known as an antigen. Hypersensitivity reactions can cause damage to the body`s own tissues and organs, and can sometimes be life-threatening. Hypersensitivity reactions are classified into four types (I-IV) based on the mechanism and timing of the immune response .

Hypersensitivity reactions can be triggered by various antigens, such as:

  • Microbes, such as bacteria, viruses, fungi, and parasites
  • Drugs, such as penicillin, aspirin, and insulin
  • Foods, such as peanuts, eggs, and milk
  • Pollen, dust mites, animal dander, and insect venom
  • Transplanted organs or tissues
  • Self antigens, such as in autoimmune diseases

Hypersensitivity reactions can affect different parts of the body, such as:

  • Skin, causing rashes, hives, blisters, or eczema
  • Respiratory system, causing asthma, hay fever, or anaphylaxis
  • Blood vessels, causing vasculitis or shock
  • Joints, causing arthritis or gout
  • Kidneys, causing glomerulonephritis or nephrotic syndrome
  • Nervous system, causing multiple sclerosis or Guillain-Barré syndrome

Hypersensitivity reactions can be diagnosed by various methods, such as:

  • Skin tests, which involve applying a small amount of antigen to the skin and observing for a reaction
  • Blood tests, which measure the levels of antibodies or immune cells in the blood
  • Biopsy, which involves taking a sample of tissue and examining it under a microscope
  • Challenge tests, which involve giving a small dose of antigen orally or intravenously and monitoring for symptoms

Hypersensitivity reactions can be treated by various methods, such as:

  • Avoiding or eliminating the antigen that causes the reaction
  • Taking medications that suppress or modulate the immune response, such as antihistamines, corticosteroids, or immunosuppressants
  • Receiving immunotherapy or desensitization, which involves gradually exposing the body to increasing doses of antigen to induce tolerance
  • Receiving emergency care for severe reactions, such as epinephrine injections or oxygen therapy

Hypersensitivity reactions are common and can affect anyone at any age. However, some people may have a genetic predisposition or environmental factors that increase their risk of developing hypersensitivity reactions. Hypersensitivity reactions can have a significant impact on the quality of life and well-being of affected individuals. Therefore, it is important to understand the causes, mechanisms, types, and management of hypersensitivity reactions.