▁may ▁contribute ▁to ▁the ▁excess ive ▁dry ness ▁of ▁the ▁skin ▁and ▁the ▁loss ▁of ▁the ▁bar rier ▁function ▁of ▁normal ▁skin . ▁It ▁may ▁be ▁possible ▁that ▁the ▁fil ag gr in ▁mut ations ▁and ▁the ▁loss ▁of ▁the ▁normal ▁skin ▁bar rier ▁expose ▁cre v ices ▁that ▁make ▁it ▁possible ▁for ▁St ap hy loc oc cus ▁a ure us ▁to ▁colon ize ▁the ▁skin . ▁At op ic ▁e cz ema ▁is ▁often ▁associated ▁with ▁gen etic ▁defect s ▁in ▁gen es ▁that ▁control ▁all erg ic ▁responses . ▁Thus , ▁some ▁investig ators ▁have ▁proposed ▁that ▁at op ic ▁e cz ema ▁is ▁an ▁all erg ic ▁response ▁to ▁increased ▁St ap hy loc oc cus ▁a ure us ▁colon ization ▁of ▁the ▁skin . ▁A ▁hall mark ▁indicator ▁of ▁at op ic ▁e cz ema ▁is ▁a ▁positive ▁“ w he al - and - f lare ” ▁reaction ▁to ▁a ▁skin ▁test ▁of ▁S . ▁a ure us ▁ant ig ens . ▁In ▁addition , ▁several ▁studies ▁have ▁documented ▁that ▁an ▁Ig E - medi ated ▁response ▁to ▁S . ▁a ure us ▁is ▁present ▁in ▁people ▁with ▁at op ic ▁e cz ema . ▁ ▁Ch anges ▁in ▁pre val ence ▁ ▁In ▁adult s , ▁the ▁pre val ence ▁of ▁Ig E ▁sens it ization ▁to ▁all erg ens ▁from ▁house ▁dust ▁m ite ▁and ▁cat , ▁but ▁not ▁grass , ▁seem ▁to ▁decrease ▁over ▁time ▁as ▁people ▁age . ▁However , ▁the ▁bi ological