"The hygiene hypothesis is actually quite controversial because it's thought that our exposure to microbes isn't the only factor," says Cody Warren, a virologist and immunologist who is a postdoctoral fellow at the University of Colorado Boulder.  
Kafukufuku wa ukhondo, hygiene hypothesis, amabweretsa maganizo osiyanasiyana pomwe ena amati kukhala osabisika ku tizilombo toyambitsa matenda si chifukwa chokha," anatero a Cody Warren, wowona za tizilombo toyambitsa matenda komanso chitetezo mnthupi yemwe anali dotolo wa ku sukulu ya ukachenjede ya Colorado Boulder.