If you have a sinus infection (which is when I've done it), I did it a 3x a day. Washing your sinuses out is a great way to keep those microbes flushing. I have no history with doing it on the regular... there are certainly different rushes for different people! I couldn't imagine it would do your sinuses harm to do it for a little bit. Maybe Miss Cast has experience with doing it nasally for an extended period? Miss Cast?