For the Acapella, the function of the vibratory pieces degrades over time. I was amazed at how much when I did my first replacement - the old one was on the highest setting, and I had to back off to just over half. Now, when I get to the highest setting, I know it will soon be time to order a new one.

For the Pari cups, or any other nebulizer cups, the repeated boiling (or alcohol) degrades the plastic over time. Recommendations for replacement vary from 2 to 6 months. Microscopic cracks and pits for in the plastic, giving bacteria fun places to hide. In addition, I become concerned about whether microscopic particles of plastic are finding their way into my lungs as it wears. So, I wash with HOT water and soap after every use, sterilize after 6-8 uses or weekly. And I discard after 10-12 sterilizations.

All that said, I use sidestream nebulizers from the hospital supply house, not Pari Sprint or AeroEclipse types, so they are not that expensive in the grand scheme of things - around $10 each with new tubing.