Type IV hypersensitivity reaction ... Type IV hypersensitivity or delayed hypersensitivity reaction occurs 48–72 hours after exposure to the allergen. This ...DermNetprovidesGoogleTranslate,afreemachinetranslationservice.Notethatthismaynotprovideanexacttranslationinalllanguageslogo-newThispagewasprintedon18/8/2021HomeTopicsA–ZImagesBrowseDermDiagGlossaryQuizzesAboutContactJobsDonatebreadcrumbsHome»TopicsA–Z»AllergiesexplainedAllergiesexplainedAuthor:AJSykes,MedicalRegistrar,AucklandCityHospital,Auckland,NewZealand.Editors:DermNetNewZealandEditorinChief,AmandaOakley,Dermatologist,Hamilton,NewZealand;PeterStorey,ClinicalImmunologistandAllergySpecialist,AucklandCityHospital,Auckland,NewZealand.Copyeditor:MariaMcGivern.March2017.Allergiesexplained—codesandconceptsopenSynonyms:Hypersensitivityreaction,Allergicorhypersensitivityconditions,Hypersensitivityresponse,Allergy-generalinformationCategories:ReactiontoexternalagentSubcategories:TypeIhypersensitivity,Anaphylaxis,TypeIIhypersensitivity,Autoimmunediseases,TypeIIIhypersensitivity,TypeIVhypersensitivity,Delayedtypehypersensitivity,TypeVhypersensitivityICD-11:4A8Y,4A44.92,4A85.2Z,EB000,NE80.3,4A84.Z,EK00.Y,EK00.Z,EK10SNOMEDCT:12263007,90092004,83699005,28031001Whatisanallergy?Allergyisanabnormalresponseofthebodytoaforeignbody,knownasanantigen.Itinvolvestheimmunesystemrecognisingthisantigenandmountingoneoffourtypesofresponse,whicharedetailedbelow.Allergyisalsoknownasa‘hypersensitivityreaction’ora‘hypersensitivityresponse’.Thisarticleusesthetermsallergyandhypersensitivityinterchangeably.Anallergyreferstotheclinicalsyndromewhilehypersensitivityisadescriptivetermfortheimmunologicalprocess.Howisanallergydifferenttointolerance?Intolerancereferstoanindividual’sabilitytohandledifferenttypesoffoodordrink.Foodintoleranceisnotatrueallergy,inthatthereisnoclearlydefinedimmuneresponseandthesymptomsthatoftendeveloponlyaffectthedigestivetract.Anintoleranceisnormallyfoundinthecontextofadeficiencyincertainenzymesthatbreakdownthecomponent