Editing Allergy (section)

===Skin===
Substances that come into contact with the skin, such as [[latex]], are also common causes of allergic reactions, known as [[contact dermatitis]] or eczema.<ref name="Natural rubber latex allergy: a problem of interdisciplinary concern in medicine"/> Skin allergies frequently cause [[rash]]es, or swelling and inflammation within the skin, in what is known as a "[[wheal response|wheal]] and flare" reaction characteristic of hives and [[angioedema]].<ref name="Urticaria and angioedema: a practical approach"/>

With insect stings, a large local reaction may occur in the form of an area of skin redness greater than 10&nbsp;cm in size that can last one to two days.<ref name=Lud2015>{{cite journal | vauthors = Ludman SW, Boyle RJ | title = Stinging insect allergy: current perspectives on venom immunotherapy | journal = Journal of Asthma and Allergy | volume = 8 | pages = 75–86 | date = 2015 | pmid = 26229493 | pmc = 4517515 | doi = 10.2147/JAA.S62288 | doi-access = free }}</ref> This reaction may also occur after [[immunotherapy]].<ref>{{cite book| veditors = Slavin RG, Reisman RE |title=Expert guide to allergy and immunology|date=1999|publisher=American College of Physicians|location=Philadelphia|isbn=978-0-943126-73-9|page=222|url=https://books.google.com/books?id=QhNRrAeXdbAC&pg=PA222}}</ref>

The way the body responds to foreign invaders on the molecular level is similar to how  allergens are treated even on the skin. The skin forms an effective barrier to the entry of most allergens but this barrier cannot withstand everything that comes at it. A situation such as an insect sting can breach the barrier and inject [[allergen]] to the affected spot. When an allergen enters the epidermis or dermis, it triggers a localized allergic reaction which activates the mast cells in the skin resulting in an immediate increase in vascular permeability, leading to fluid leakage and swelling in the affected area.<ref name="New York: Garland Science">{{cite book |last1=Janeway |first1=CA |last2=Travers |first2=P |last3=Walport |first3=M |title=The Immune System in Health and Disease |chapter=Effector mechanisms in allergic reactions |date=2001 |publisher=New York: Garland Science |edition=5th |url=https://www.ncbi.nlm.nih.gov/books/NBK27112/}}</ref> Mast-cell activation also stimulates a skin lesion called the wheal-and-flare reaction.<ref name="Wheal and Flare">{{cite web |last1=Robinson |first1=Dan |title=Wheal and Flare |url=https://ent-clinics.com.au/wheal-and-flare/ |website=ENT Clinics}}</ref> This is when the release of chemicals from local nerve endings by a nerve axon reflex, causes the [[Vasodilation|vasodilatations]] of surrounding cutaneous blood vessels, which causes redness of the surrounding skin.<ref name="Wheal and Flare"/>

As a part of the allergy response, the body has developed a secondary response which in some individuals causes a more widespread and sustained edematous response.<ref name="New York: Garland Science"/> This usually occurs about 8 hours after the allergen originally comes in contact with the skin. When an allergen is ingested, a dispersed form of wheal-and-flare reaction, known as urticaria or hives will appear when the allergen enters the bloodstream and eventually reaches the skin.<ref name="New York: Garland Science"/><ref>{{cite web |last1=Oakley |first1=Amanda |title=Urticaria (hives): A complete overview |url=https://dermnetnz.org/topics/urticaria-an-overview |website=DermNet®|date=26 October 2023 }}</ref> The way the skin reacts to different allergens gives allergists the upper hand and allows them to test for allergies by injecting a very small amount of an allergen into the skin.<ref name="New York: Garland Science"/> Even though these injections are very small and local, they still pose the risk of causing systematic anaphylaxis.<ref name="New York: Garland Science"/>