two factors. 1 is you. how you treat the system, how often you wash it, how rough you are, what kind of procedures you use to clean the unit or attach etc. your physical activity how much are you in the sun or out doors, etc.

The 2nd variable is the design of the system itself. How well was the system ventilated .. Sometimes they can make loose knots that fall apart, and other times the knots can last. The base .. Super fine swiss verse french or skin etc, What kind of knots, injection, U-looped. etc.