Laces are the literal pieces that make your shoes come together. While they are made to withstand pulling, tugging, and other strains as they are constantly tied and untied, it is important to remember that they are not as durable as the actual sneaker, and often times should be switched out.
Nowadays, a lot of shoes (especially collabs) come with alternate laces. Personally, when I’m cleaning a shoe I know to have alternate laces, I use them in re-lacing in lieu of the original laces so as to break in the different laces, give the sneakers so new flavor, and, reduce the amount of wear on the original laces. The alternate laces are there for a reason, use them! You might even find that you like using the alternate laces even more than the originals.
Of course, you don’t always have to replace the laces every time you’re cleaning your sneakers. In the cases where you might be using the same pair of laces a little more constantly, signs you should be wary of are stiffness, fraying, and stains not removed after cleaning. Laces over time can tend to get stiff around where they were looped through eyelets and where they are tied. While some stiffness over time is inevitable, this is where washing them on a somewhat consistent basis is important, because a good washing routine can slow the effects of stiffness and any staining from bent/tied portions of lace. When laces become stiffer, they can lose their durability over time, which leads to fraying.
Fraying laces are a problem and a warning that your laces are soon in jeopardy of coming apart. When we were younger and tore up Superstars and Phat Farms on the playground, it was okay for our laces to be raggedy and torn up. But remember how hard it was to tie your shoes in the mornings because the laces was nothing but strings? If I ever see your laces in this dire state, I might just take your shoes off you and have your walk home in your socks. When you first see signs of your laces coming apart, replace them. Signs of fraying usually appear around the eyelets and at the tips of the laces. We just talked about alternate laces. If you don’t have alternate laces handy, you can find laces almost anywhere that also happens to sell candy. Laces are also generally cheap, so it won’t cost much time or money to find replacement threads. If you want to be a snob about it, you can even find custom/designer/alternative laces on the internet, and they won’t cost too much more than the run of the mill Kiwi laces two aisles down from the Kit-Kats at the 7-Eleven.
Stains that do not come off after washing are another problem, and usually comes back to how often you are taking care of your laces. Stains and marks that don’t come off can be a problem in the future, as they can collect more dirt and grime, become stiffened, and ultimately make it a little more difficult to tie and lace them. Depending on the color/texture of the laces (raw leather/suede, cotton, canvas, etc) in comparison to its shoe, this may happen sooner than later, and through no real fault of your own outside of normal use. Still, you should pay attention to it. If your laces are not cleaning like they used to, this should be taken as a sign to switch them out for a fresh pair.