As your mask and other CPAP accessories start to age the materials they are made of start to break down. Your mask and hose absorb dirt even if you clean it daily.  The silicon interface starts to lose it’s flexibility and your mask seal will worsen, which will affect your sleep therapy.  As your mask ages, this silicon will develop micro abrasions, a tiny microscopic tear or hole, that become breeding grounds for germs. After six months, even a freshly cleaned mask retains germs.