He needs to wash the mask everyday, or every other day at the very least. Bacteria and other stuff builds up in the mask, which can cause other health problems.
The mask is probably leaking because he doesn't have it on tight enough, or the mask or hose is wearing out and needs to be replaced. I found with mine that there is a very little leeway between having it tight enough for it not to leak, and loose enough to make it comfortable (for lack of a better word, as it is not comfortable). Sometimes in the morning, it leaks a little and makes a farting sound.
But I never got sick. I get a new mask about every 6 months. 
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