Editing Allergen (section)

{{short description|Type of antigen that produces an abnormally vigorous immune response}}
{{about|the antigen|the Irish-registered pharmaceutical company|Allergan}}
{{Use dmy dates|date=August 2015}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
An '''allergen''' is an otherwise harmless substance that triggers an [[allergic reaction]] in sensitive individuals by stimulating an [[immune response]].

In technical terms, an allergen is an [[antigen]] that is capable of stimulating a [[type-I hypersensitivity]] reaction in [[atopy|atopic]] individuals through [[immunoglobulin E]] (IgE) responses.<ref>{{cite book | vauthors = Goldsby RA, Kindt TJ, Kuby J, Osborne BA |title=Immunology |date=2003 |publisher=W.H. Freeman |location=New York |isbn=978-0-7167-4947-9 |edition=5th}}</ref> Most humans mount significant immunoglobulin E responses only as a defense against [[parasitic infection]]s. However, some individuals may respond to many common environmental antigens. This hereditary predisposition is called [[atopy]]. In atopic individuals, non-parasitic antigens stimulate inappropriate IgE production, leading to type I hypersensitivity.{{citation needed|date=March 2022}}

Sensitivities vary widely from one person (or from one animal) to another. A very broad range of substances can be allergens to sensitive individuals.