I think mine break down more from washing than wearing. I should probably switch to hand wash, but that's a huge PITA, so I machine wash gentle and hang dry everything. Hard to say how long they last, I've had some last for several years (some may be 10 years old or more, but those are on trainer duty only now). It's more about number of washings IMO, but again, super hard to say because I have so many pairs I may go a month or more before wearing the same pair again.

Basically I didn't answer your question...