While we’ve all heard that running shoes break down after logging lots of miles (about 300 to 350), you may still be holding on to your fave pair. (They fit just right! They’re so cushy!) Not a good idea. “Glue has a tendency to break down under ultraviolet light, as do the other materials that make up the shoe,” says Andrew Kastor. So even if your sneaks have only 150 miles on them but are more than two years old, recycle them (try oneworldrunning.com or recycledrunners.com), because chances are they’ve already started deteriorating. And as a rule of thumb, always keep tabs on how many miles you’ve logged on them—tedious, but hey, you’ll be proud of how far you’ve gone.