Anallergy(过敏反应)isastrongreactiontoasubstance.Manythingscancauseallergies.Themostcommoncauseispollen(花粉)whichisusuallyproducedbytreesinthespringgrassesinthesummerandweedsinthefallaspartoftheirreproductiveprocess.
Othercausesincludeorganismschemicalsplantsanddeadskinparticles(微粒)fromdogsandcatscanalsocauseallergicreactions.Socaninsectstingsandsomefood.
Themostcommonkindofallergicreactionsisitchy(痒的)wateryeyesandablockedorwaterynose.Allergiescanalsocausereditchyskin.Somereactionscanbelife-threateningforexamplewhenbreathingpassagesbecomeblocked.
Itisnotalwayseasytoavoidallergies.Drugsmayofferaneffectivetreatment.Anothertreatmentusedinsomecasesiscalledimmunotherapy(免疫疗法).Apatientisinjectedwithsmallamountsoftheallergy-causingsubstance.Theideaisthatlargerandlargeramountsaregivenovertimeuntilthepatientdevelopsaresistanceinhisbody.
IntheUnitedStatesexpertsestimatethatupto8%ofyoungchildrenhavefoodallergies.Everyyeartheseallergiescauseabout30000caseswithseverereactionsthatrequireimmediatetreatment.Itcanresultinbreathingtroubleandinsomecasesdeath.Itissaidthatabout100to200peoplewilldie.Itsaysmostofthereactionsarecausedbypeanutsandtreenutslikewalnuts.
Peoplecanalsobeallergictomedicines.TheAmericanAcademyofAllergyAsthmaandImmunologysaysabout10%ofbadreactionstocommonlyusedmedicinesareallergic.Inotherwordsaperson’simmunesystemoverreactsandproducesanallergicreaction.Themostcommonreactionsincludeskinrashes(皮疹)itchingbreathingproblemsandswellinginareassuchastheface.
【小题1】Allergiesseldomoccurinwinterbecause______.
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