Medical Mnemonics: Types of Hypersensitivity Reactions

Medical Mnemonic: Types of Hypersensitivity Reactions - "ACID"

Medical Mnemonics: Internal Medicine Board Review – Hypersensitivity Recations


There are four types of hypersensitivity reactions.
  • Type I is IgE-mediated and occurs very quickly after exposure. It is associated with allergens such as bee stings, peanuts, and certain medications, to name a few. This can lead to a life-threatening condition called anaphylaxis.
  • Type II hypersensitivity reactions are cytotoxic/antibody-mediated. Some examples in this category are hemolytic reactions, goodpasture syndrome and hyperacute graft rejection.
  • Type III is known as immune complex/IgG/IgM mediated and includes certain diagnoses like hypersensitivity pneumonitis, systemic lupus erythematosus, polyarteritis nodosa and serum sickness.
  • Type IV is known as delayed or cell-mediated hypersensitivity reaction. Examples include chronic graft rejections, purified protein derivative (PPD), latex, nickel and poison ivy.


A quick mnemonic to use to remember these is ACID:
  • Type I – Allergic
  • Type II – Cytotoxic
  • Type III – Immune complex deposition
  • Type IV – Delayed


This is the second in our series of Medical Mnemonics Monday posts. You can all previous and future medical mnemonics here.

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