AllergicReactionWhathappenswhenyouhaveanallergicreaction?TypesWhatarethefourtypesofallergicreactions?TriggersWhatarethetriggersofallergicreactions?CenterWhatAretheFourTypesofAllergicReactions?CenterWhathappenswhenyouhaveanallergicreaction?Allergistsrecognizefourtypesofallergicreactions:TypeIoranaphylacticreactions,typeIIorcytotoxicreactions,typeIIIorimmunocomplexreactionsandtypeIVorcell-mediatedreactions.Allergicreactionsareexaggeratedsensitivities(hypersensitivereactions)thatoccurwhenyourimmunesystemrespondsabnormallytocommonsubstancessuchaspollen,dustandcertainfoods. Thesesubstances,calledallergens,areharmlessinamajorityofpeople. Butforthosewhoareallergic,theycancausereactionsuponskincontactorwhentheyarebreathed,swallowedorinjected. Allergicreactionsarequitecommonandmayhappensecondstohoursaftercontactwiththeallergen.Somereactionsmaytakemorethan24hourstoappear.Thoughmanyallergicreactionsaremild,othersmaybedangerousorlife-threatening.Theymaybelocalized,involvingasmallpartofthebodyormayaffectalargeareaorthewholebody.Certainmetaljewelleryorcertaincosmeticsmaycauseskinrashinsome,forexample.Otherssneezeuncontrollablyonexposuretodustorpollen. Anallergicreactionbeginswhenyoutouch,inhaleorswallowanallergen.Inresponsetothistrigger,thebodystartsmakingatypeofproteincalledIgEorimmunoglobulinE. IgEmoleculesbindwiththeallergenmoleculesinanantigen-antibodyreaction.Thisattachmentoftheantigenandantibodyleadstothereleaseofsomechemicals(suchashistamine)inthebody.Thesechemicalscausetheinflammatorysymptomsofallergicreactionssuchasrashes,itchingandsneezing. Whatarethefourtypesofallergicreactions?Allergenscancauseallergicreactionsuponskincontact,whentheyarebreathed,swallowedorinjected.TwoBritishimmunologists,CoombsandGell,haveclassifiedallergicreactionsintofourtypes,TypeI,II,IIIandIV. TypeI,IIandIIIallergicreactionsarecalledimmediatetypesofallergicreactionsbecausetheyoccurwithintwenty-fourhoursofexposuretotheallergen.TypeIVreactionstypicallyoccurafter24hoursofexposureandarecalleddelayeda