Type I hypersensitivity


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Type I hypersensitivity

Immune system

Introduction to the immune system

Introduction to the immune system



Innate immune system

Innate immune system

Complement system

Adaptive immune system

T-cell development

B-cell development

MHC class I and MHC class II molecules

T-cell activation

B-cell activation and differentiation

Cell-mediated immunity of CD4 cells

Cell-mediated immunity of natural killer and CD8 cells

Antibody classes

Somatic hypermutation and affinity maturation

VDJ rearrangement

Contracting the immune response and peripheral tolerance

B- and T-cell memory

Anergy, exhaustion, and clonal deletion


Hypersensitivity reactions

Type I hypersensitivity

Type II hypersensitivity

Type III hypersensitivity

Type IV hypersensitivity


Type I hypersensitivity


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Type I hypersensitivity

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Asthma p. 698

type I hypersensitivity p. 110


type I hypersensitivity p. 110

Hay fever

type I hypersensitivity p. 110

IgE antibodies p. 103

type I hypersensitivity p. 110


type I hypersensitivity p. 110

Type I hypersensitivity p. 110

IgE antibodies and p. 103

Type I hypersensitivity reactions

mast cells and p. 411

Urticaria p. 487, 489

as type I hypersensitivity p. 111

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Content Reviewers

Rishi Desai, MD, MPH


Tanner Marshall, MS

Having a hypersensitivity means that someone’s immune system has reacted to something in such a way that it ends up damaging them, as opposed to protecting them.

There are four different types of hypersensitivities, and in the first type or type one, the reactions rely on Immunoglobulin E, or IgE antibody, which is a specific type of antibody - the other major ones being IgG, IgA, IgM, and IgD.

So because IgE is involved with type one hypersensitivity reactions they are also called IgE-mediated hypersensitivities.

This type of reaction is also sometimes called immediate hypersensitivities, because the reaction happens super fast—on the order of minutes.

So most allergic reactions are IgE-mediated, and therefore most allergies are type I hypersensitivity reactions.

Allergy” comes from the Greek Allos which roughly means “other” and ergon which means “reactivity”.

Essentially, allergies are reactions to molecules from outside your own body that most people don’t react to—and these are specific molecules from things you might breathe or take in like foods, animal dander, bee stings, mold, drugs or medications, and pollen.

You can also mount an allergic reaction to things you come in contact with on your skin like latex, lotions, and soaps.

These specific molecules are also called antigens, and when they cause an allergic reaction, they’re called allergens.

An allergic reaction happens in two steps, a first exposure, or sensitization, and then a subsequent exposure, which is when it gets a lot more serious.

People that react to these allergens usually have a genetic predisposition to having over-reactions to unknown molecules or allergens.


Type I hypersensitivity is a type of allergic reaction that occurs when the immune system overreacts to an otherwise harmless substance, such as pollen, dust, or certain foods. It is characterized by the rapid release of immunoglobulin E (IgE) antibodies in response to the allergen. In Type I hypersensitivity, the allergen triggers the production of IgE antibodies, which bind to specific receptors on mast cells and basophils in various tissues throughout the body. The next time the person is exposed to the same allergen, it triggers the release of histamine and other chemicals, causing the typical symptoms of an allergic reaction. Common examples of Type I hypersensitivity reactions include allergic rhinitis, asthma, hives, and anaphylaxis. Treatment options include avoiding the allergen, taking antihistamines and other medications, and in severe cases, using epinephrine to manage anaphylaxis.


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