▁D iff use ▁al ve olar ▁damage ▁can ▁be ▁a ▁cause ▁of ▁ac ute ▁resp ir atory ▁dist ress ▁synd rome ( AR DS ) ▁a ▁severe ▁infl am mat ory ▁disease ▁of ▁the ▁lung . ▁▁ ▁In ▁ast h ma , ▁the ▁bron chi oles , ▁or ▁the ▁" b ott le - ne cks " ▁into ▁the ▁sac ▁are ▁restricted , ▁causing ▁the ▁amount ▁of ▁air ▁flow ▁into ▁the ▁l ungs ▁to ▁be ▁greatly ▁reduced . ▁It ▁can ▁be ▁triggered ▁by ▁ir rit ants ▁in ▁the ▁air , ▁phot och em ical ▁sm og ▁for ▁example , ▁as ▁well ▁as ▁subst ances ▁that ▁a ▁person ▁is ▁all erg ic ▁to . ▁ ▁Chron ic ▁bron ch itis ▁occurs ▁when ▁an ▁abund ance ▁of ▁m uc us ▁is ▁produced ▁by ▁the ▁l ungs . ▁The ▁production ▁of ▁this ▁subst ance ▁occurs ▁naturally ▁when ▁the ▁lung ▁t issue ▁is ▁exposed ▁to ▁ir rit ants . ▁In ▁chron ic ▁bron ch itis , ▁the ▁air ▁pass ages ▁into ▁the ▁al ve oli , ▁the ▁resp ir atory ▁bron chi oles , ▁become ▁c log ged ▁with ▁m uc us . ▁This ▁causes ▁increased ▁c ough ing ▁in ▁order ▁to ▁remove ▁the ▁m uc us , ▁and ▁is ▁often ▁a ▁result ▁of ▁extended ▁periods ▁of ▁expos ure ▁to ▁cig aret te ▁smoke . ▁ ▁Hyp ers ens itivity ▁p neum on itis ▁ ▁Struct ural ▁Al most ▁any ▁type ▁of ▁lung ▁tum or ▁or ▁lung ▁cancer ▁can ▁compress ▁the ▁al ve oli ▁and ▁reduce ▁gas