Summarize this article:

Tufted rugs are held together by a layer of latex glue that secures the tufts and prevents them from falling out. If your rug is particularly old, this layer of glue will show signs of cracking and crumbling, meaning that the tufts are no longer secure. If you notice patches on the underside of your rug that are missing glue, be extra careful when cleaning that portion of the rug. Being too aggressive will lead to fibers falling out and the creation of bare patches.

Summary:
Check the underside for peeling.