Type I hypersensitivity

00:00 / 00:00


Type I hypersensitivity


0 / 15 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

4 pages


Type I hypersensitivity

of complete


USMLE® Step 1 style questions USMLE

of complete

A 40-year-old woman comes to the emergency department after developing dyspnea, hives, and audible wheezing. The patient accidentally ingested peanuts an hour ago,  to which she has a known allergy. Which of the following is the most likely underlying mechanism of this patient’s condition?  

Memory Anchors and Partner Content

External References

First Aid








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

External Links


Content Reviewers

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.


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.


Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.